In his first major league at-bat on April 8, 1986, on his first swing, Clark hit a home run—off future Hall of Fame member Nolan Ryan. A few days later, Clark also homered in his first home game at Candlestick Park (he debuted at age 22, wearing the number 22, playing first base). An elbow injury cost Clark 47 games in his rookie season. Clark finished his rookie year with a .287 batting average. In his first full season in , Clark had a .308 batting average. Clark was voted the starting first baseman for the NL All-Star team every season from 1988 through 1992. In , Clark was the first Giants' player to drive in 90 or more runs in consecutive seasons since Bobby Murcer from -. In , Clark batted .333 (losing the batting title to Tony Gwynn on the final day of the season) with 111 runs batted in (RBIs). Clark finished second in the NL Most Valuable Player voting to Giants teammate Kevin Mitchell. In , Clark and the Giants defeated the Chicago Cubs in the National League Championship Series (NLCS). In Game 1, Clark had already hit a solo home run. 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." The first pitch was a fastball high and inside which Clark sent into the street beyond right field for a grand slam. Afterwards, pitchers began to cover their mouths with their gloves when having conversations on the pitcher's mound. (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.) 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. The Giants went on to face the Oakland Athletics in the 1989 World Series, but were swept. In the only World Series appearance of his career, Clark failed to