[10] Along with Harper, starting pitcher Jeremy Hellickson,[11] catcher Matt Wieters,[12] infielder Mark Reynolds,[13] and relievers Joaquín Benoit,[14] Tim Collins,[15] Kelvin Herrera,[16] and Greg Holland[17] became free agents after the 2018 season.

[30] Ten days after signing Suzuki, the Nationals made another trade to bolster their catching corps, sending pitcher Jefry Rodríguez, a minor league outfielder, and a player to be named later to the Cleveland Indians for veteran Yan Gomes.

[76] Having already recalled infielder Adrián Sánchez from the Class-AAA Fresno Grizzlies to replace Turner on the roster,[77] the Nationals optioned Noll after the April 3 game to make room for the activation of veteran utilityman Howie Kendrick from the injured list.

[84] After a third straight strong start for the Nationals in the series, this one provided by Scherzer, Suero allowed a two-out RBI double to rookie Jason Martin in the ninth, sending the home team to a 4–3 loss in the April 14 rubber game.

[88] Heading to South Florida for a series against the division-rival Miami Marlins on April 19, the Nationals made another change in their bullpen, sending Williams to the injured list with a right shoulder sprain and recalling right-hander Austin L. Adams from Fresno.

[92] After optioning Austin L. Adams back to Fresno and recalling Noll as an extra infielder with Rendon dealing with soreness after a pitch struck his upper arm, Washington dropped yet another series opener on April 22 as they traveled to Denver for three games against the Colorado Rockies, as home runs by Raimel Tapia, Nolan Arenado, and former National Mark Reynolds proved too much for the visitors to overcome.

[102] After placing first baseman Ryan Zimmerman on the 10-day injured list with plantar fasciitis in his right foot, the Nationals were greeted with six unanswered San Diego runs to start the April 28 game, as the home team got just three innings out of Hellickson.

[105] Ahead of another loss on April 30, the Nationals finally placed Rendon on the 10-day injured list as he continued to reel from his hit-by-pitch arm injury from the Marlins series, and they selected the contract of left-hander Dan Jennings from Harrisburg, designating Austin L. Adams for assignment to clear space on the roster.

[110] The Nationals activated third baseman Anthony Rendon from the injured list on May 7, optioning top infield prospect Carter Kieboom back to Fresno after he committed four errors in 11 major league games,[111] and also recalled right-handed pitcher Erick Fedde from the Class-AA Harrisburg Senators.

[123] The Nationals attempted a comeback after right-hander Max Scherzer was shelled for three runs early on May 18, but Brian Dozier was tagged out trying to score from third on an errant pitch that ricocheted back to reliever Carl Edwards Jr., then the home bullpen melted down.

[127] Heading to New York City for another series against the Mets, on May 20, the Nationals designated Dan Jennings for assignment after he appeared in eight games out of their bullpen, activated Sipp from the injured list, and claimed right-handed pitcher Javy Guerra off waivers from the Toronto Blue Jays.

[132] The Nationals trailed by two runs heading into the eighth inning in the final game of the set on May 23, but after first baseman Howie Kendrick and manager Dave Martinez were ejected for arguing a checked-swing call, the team rallied and got a two-out, two-run single by Parra, pinch-hitting for Strasburg, to take the lead.

[144] Scherzer pitched well in the series finale and exited the game with a one-run lead, but the Marlins scored two unearned runs as Adams and Turner committed ill-timed fielding errors, and Miami salvaged the set by delivering the Nationals a 3–2 loss.

Despite another eighth-inning hiccup on May 28 as Barraclough gave up a two-run home run, Doolittle bounced back from a pair of rough outings, showing off a tweaked delivery as he secured a save and a win for Strasburg, who outdueled Atlanta ace Max Fried with seven strong innings.

[165] Following another poor relief appearance by Barraclough, who gave up three runs in the ninth inning while only recording one out,[166] the Nationals placed him on the 10-day injured list with right radial nerve inflammation and summoned utilityman Adrián Sánchez the next morning.

[167] Washington ran away with the fourth and final game of the series 15–5, with Aníbal Sánchez pitching effectively and first baseman Matt Adams supplying almost half the offense, with seven RBIs on a three-run home run off reliever Zack Godley and a grand slam off Stefan Crichton.

While taking bunting practice on June 18 before that day's game was officially rained out, Scherzer fouled a ball back into his face, leaving him with a broken nose and a swollen right eye—for the heterochromatic ace, his blue eye.

Showing a marked improvement in his velocity from the previous season as his fastball topped 95 miles per hour (153 km/h) throughout his six innings, Voth pitched well, striking out a career-high seven batters while allowing just two runs, both solo homers, on four hits.

Scherzer struck out 14 over eight innings in his start to secure the series win,[188] after the loss on June 29, in which Voth struggled en route to a fifth-inning hook and then Rainey and left-handed reliever Tony Sipp combined to lose the late lead.

[200] Pinch-hitter Howie Kendrick, inserted into the game for a favorable matchup against the left-hander Diekman, plated two more runs with a double of his own before Doolittle pitched a scoreless ninth inning to secure the series win and send the Nationals victorious into the break.

[222] In the July 27 contest, trying to even the series against former Cy Young Award-winning southpaw Clayton Kershaw, Martinez deployed Grace as a two-inning "opener" against the Dodgers' lefty-heavy lineup before bringing in the day's presumptive starting pitcher, Ross, who was known to struggle against left-handed hitters.

Washington general manager Mike Rizzo acknowledged that he was constrained by the team's commitment not to exceed the competitive balance threshold, as it had in 2017 and 2018,[237] and he noted that Hudson, Elías, and Strickland were added without the Nationals having to give up any of their top prospects,[238] with the highest-ranked minor league player they traded being Class-AAA left-handed reliever Taylor Guilbeau as part of Seattle's return.

On August 9, a resurgent Strasburg set a new franchise high in strikeouts[note 16] but ended up with a no-decision after closer Sean Doolittle blew a three-run lead on a Todd Frazier home run in the ninth inning, then right fielder Adam Eaton missed a Michael Conforto line drive that fell in for a walk-off single.

[260] While Doolittle recorded the save, the Reds scored two off the struggling Nationals closer, on a home run by Phillip Ervin and a double by Votto, and put the go-ahead runner on base before VanMeter popped out to end it.

[277] With ace Max Scherzer returning from a shoulder injury, Dozier coming back from paternity leave, and McGowin and Adrián Sánchez optioned in a corresponding move, Washington won the series, again holding the Pirates to one run, with a 7–1 win on August 22.

[290] With rosters expanding, the Nationals activated a slew of veterans from the injured list: first baseman Ryan Zimmerman and pitchers Sean Doolittle, Jeremy Hellickson, and Austin Voth, all of whom had completed rehab assignments in the minor leagues the previous month.

The loss stretched into a losing streak in Atlanta, as Max Fried,[297] Dallas Keuchel,[298] and Julio Teherán[299] smothered the Nationals' offense over three consecutive starts and Washington was unable to come all the way back against the Braves bullpen.

Atlanta manager Brian Snitker began shouting and was ejected from the game after the umpires ruled that the play was not a hit-by-pitch but a strike, because Culberson had squared around to bunt and hadn't pulled back his bat at the time he was hit by Rodney's fastball.

The Nationals rebounded to salvage the series finale on September 15, benefiting from a pristine start by Aníbal Sánchez and scoreless relief innings by Hunter Strickland and Doolittle,[313] as well as an offensive resurgence that sent Fried to a third-inning exit and a loss.

[394] Over the preceding month, Rendon – known for disliking media attention – had expressed the view that he would prefer to spend the 2019 all-star break at home in Houston, resting and enjoying the company of family and friends out of the spotlight, although after his selection was announced he admitted that it actually meant a great deal to him.