Despite limited experience at third base, Boswell made his major league debut on September 18 at third against the Los Angeles Dodgers.

[2] The following day, he hit his first major league home run off Hall of Famer Don Drysdale.

He batted .246 with four home runs and ten RBIs through June 24 when a broken finger sidelined him for the month of July and most of August.

By season's end, he managed to raise his batting average up to .261 to be recognized as the Topps All-Star Rookie Team second baseman.

[5] Boswell batted .250 with two home runs and eleven RBIs through the end of May when he left the club for a two-week military commitment.

At the time, the Mets were 19–23, in third place in the National League East, nine games back of the Chicago Cubs.

In his first game back, Boswell scored the only run in Gary Gentry's 1–0 shutout of the Philadelphia Phillies.

[6] Two days later, his two out single in the ninth inning drove in the tying and winning runs of the Mets' 6–5 victory over the Phillies.

The Mets were losing the first game of the set 3–1 to Ferguson Jenkins when Boswell pinch hit for Jerry Koosman to lead off the ninth.

[9] Tom Seaver lost a pitchers' duel with Bill Hands in the series opener when it was the Cubs' turn to host the Mets July 14–16.

[10] The following day, Boswell's solo home run that put the Mets up 5–1 turned out to be the margin of victory in their 5–4 win.

[16] The following day, Boswell went 2-for-4 with a double, two RBIs and a run scored in the Mets' 7–1 victory that moved them a half a game back of the Cubs.

Boswell ended it in the twelfth with an RBI single that put the Mets in first place for the first time in franchise history.

Heading into May, Boswell was batting below .200 when he went 3-for-5, and scored the game-winning run of the Mets' extra-innings 6–5 defeat of the Astros.

A hot month of September brought his average above .200, and on the last day of the season, Boswell went 4-for-6 with three RBIs, including the game winner.

[28] The acquisition severely diminished Boswell's role, with most of his playing time coming either at third or as a pinch hitter.