1948–1949 1948 was Caballero's first full season in the major leagues, playing 79 games during the year at third base, where he was the regular starter over
Willie "Puddin' Head" Jones, and also made 23 appearances at
second base. At the plate, Caballero had a .245 batting average, the second-lowest among the team's starters that season—higher only than catcher
Andy Seminick. Additionally, Caballero notched the team's only hit in a one-hit pitching performance by
Brooklyn Dodgers starting pitcher
Rex Barney. In the middle of the season, the Phillies promoted Caballero's former Utica manager Sawyer from their
Triple-A farm team, the
Toronto Maple Leafs of the
International League, to replace
Ben Chapman at the helm. Teammate
Robin Roberts described Caballero, as well as Hamner, Ashburn, and catcher
Stan Lopata, as having "the highest respect for [Sawyer]"—all having played under his tutelage at Utica; Caballero regressed in 1949, playing in only 22 games with the Phillies, spending the majority of his season playing second base for the Maple Leafs in Triple-A. He played in 48 games, amassing a .318 batting average (the second-highest total on the team) and eight extra-base hits.
1950: The "Whiz Kids" Entering the
Phillies' 1950 season at 22 years old, Caballero was described as having "great potential", but the Phillies wanted
Mike Goliat to take over as the everyday second baseman. and a utility infield role with the Phillies. Media reports speculated that the Phillies would challenge the Dodgers for the
National League pennant, and one of Caballero's most valuable roles as a utility player was as a
pinch runner off the
bench. In the second game of a July 25
doubleheader against the
Chicago Cubs at
Shibe Park, starting pitcher Roberts batted in the bottom of the ninth in a scoreless shutout. With
Bob Rush on the mound for Chicago, Roberts managed a
walk and was replaced on base by Caballero, who promptly took second base on a
hit and run groundout by first baseman
Eddie Waitkus. that ended with a 9–8 Phillies victory, closer
Jim Konstanty's 13th of the season. Caballero displayed his running skills again in September, replacing Goliat in the ninth inning of another game against the Cardinals, and scoring a late-inning run in place of Lopata against the
Cincinnati Reds several days later to tie a close game that the Phillies eventually lost in 18 innings. On September 26, Caballero scored another crucial run against the
Boston Braves when he pinch-ran for outfielder
Dick Sisler. Waiting on third base after advancing from first on a
Del Ennis single to center field, Jones hit a high ground ball to Boston shortstop
Sibby Sisti, who
booted the ball and allowed Caballero to score the game-tying run; the Phillies won, 8–7. Philadelphia advanced to the
1950 World Series to play the
New York Yankees, where they were defeated, four games to none. In the series, Caballero made three appearances: and for Goliat in Game 3—and one as a pinch-hitter for Konstanty in Game 4, where he struck out. For the season, Caballero appeared in 46 games and posted a .167 batting average. He played mostly second base during the 1951 season, fielding the position in 54 games. He posted only a .186 batting average at the plate and hit his only major league home run, along with 3 doubles and 2 triples in 84 games played. With 10 hits in 42 at-bats in what would be his final season in the major leagues, Caballero achieved a .238 average in the 1952 season, hitting three doubles. On June 15, Caballero had a three-hit game against the
Pittsburgh Pirates in the second game of a doubleheader, one of the top performances of his career. He also batted in three runs in one game against the Giants on September 27. ==Return to the minors==