[11] In his first major league at-bat on April 8, 1986, on his first swing, Clark hit a home run off Nolan Ryan.

Prior to a subsequent at-bat, Cubs' catcher Rick Wrona went to the mound to discuss with Greg Maddux how to pitch to Clark.

From the on-deck circle, Clark watched the conversation and read Greg Maddux's lips saying "fastball high, inside."

[12] (The Chicago Tribune's front page the next day paid tribute to his performance with a headline of "Clark's night on Addison", referring to the street outside Wrigley Field where the home runs landed.

[13]) In Game 5 of the series, Clark faced Cubs closer Mitch Williams with the score 1–1 in the bottom of the eighth inning.

Clark singled to center field to drive in two runs, breaking the tie, eventually sending the Giants to the World Series.

Clark's efforts, which included a .650 batting average and two home runs, resulted in him being named NLCS MVP.

[14] Clark had become a very durable player since his rookie year injury, setting a San Francisco record with 320 consecutive games played from September 1987 through August 1989.

[11] In January 1990, he signed a four-year, $15 million contract with the Giants, which at the time made him the highest-paid player in the majors.

[6] The Texas Rangers signed Clark to replace his former Mississippi State teammate, Rafael Palmeiro, at first base.

Clark made the American League All-Star team in 1994[6] and finished the season with a .329 batting average, the second-highest of his career.

Injuries limited his playing time to 123, 117 and 110 games from 1995 through 1997, but Clark led the Rangers to American League West Division titles in 1996 and 1998.

Clark struggled offensively in both the 1996 and 1998 postseasons, though he put together his most productive regular season in seven years in 1998 (.305, 23 HRs, 41 2Bs, 102 RBIs).

Clark signed a two-year deal with the Orioles before the 1999 season, again replacing Palmeiro, who had left Baltimore to return to Texas.

Despite being revitalized during his time with the Cardinals, he decided to retire at the end of the season, largely due to familial obligations.