In and , he started regularly on third. After the 1998 season, the Mets signed third baseman Robin Ventura, and Alfonzo was forced to move to second base. While he was upset about the move at first, he became one of the best defensive second baseman in the league from –. Alfonzo was part of the infield considered to be among the best infields in MLB history on a cover of Sports Illustrated, along with Rey Ordóñez, Robin Ventura, and John Olerud. Before the season, the Mets signed the aging Roberto Alomar, and despite Alfonzo's tremendous offensive and defensive contributions during the previous three seasons, he was forced to move back to third base. He remained strong defensively; however, he struggled on offense, and the Mets decided not to re-sign him. Alfonzo had his first opportunity to display his clutch hitting ability to a nationwide audience in the 1999 playoffs. After finishing in a tie with the Cincinnati Reds for the National League Wild Card, the Mets played a one-game playoff to decide who would go on to the division series. In his first at bat of the game, Alfonzo hit a two-run home run over the center field fence, providing the Mets with all the offense they would need as Al Leiter threw a complete game shutout. On the very next night, the Mets played the Arizona Diamondbacks in the first game of the Division Series. Facing the feared Randy Johnson, Alfonzo again homered in his first at bat of the game, this time launching a two-run shot to center field. In the ninth inning of the same game, with the score deadlocked at 4–4, Alfonzo launched a grand slam down the left field line to help seal the victory for the Mets. In , playing against the San Francisco Giants in the Division Series, Alfonzo hit a two-run homer in the ninth inning of game two, which would prove to be of immense importance as J. T. Snow launched a three-run homer in the bottom half of the inning to tie the game. The Mets would eventually win the game 5–4 in ten innings. In game three of the series, with the Mets trailing 2–1 in the bottom of the eighth inning, the Giants brought in their dominant closer Robb Nen, who had not blown a save since the All-Star break. Alfonzo responded by lining a ball down