Roberts played college baseball for the University of Oregon, where he was primarily a shortstop. After his junior year, he was made the number one overall pick in the 1972 Major League Baseball Draft by the Padres on June 6.

The following day, he signed with the Padres, and later that day made his major league debut, becoming the sixth player to go straight to the majors after being drafted without first playing in the minor leagues. He appeared in the second game of a doubleheader against the Pittsburgh Pirates, entering the game in the 12th inning at third base and going 0-for-3.

Roberts spent most of the remainder of the 1972 season as the Padres' regular third baseman. However, he was shifted to second base in mid-September following the promotion of Dave Hilton from the minors. Overall, he hit .244 with five home runs and 33 runs batted in.

With regular Tito Fuentes injured to start the season, Roberts opened the 1973 season as the Padres' regular second baseman. After five games, in which he went 1-for-16, Fuentes returned, and Roberts was sent to the bench. Over the next 17 games, Roberts played in eight, all as a pinch hitter. At the end of April, with Roberts batting .083 and without an extra-base hit, he was demoted to the minor leagues.

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