The most significant portion of his career, both in terms of tenure and significance, was with the Dodgers. After 6 years in the majors, he was traded from the Senators to the Dodgers in a 7-player deal, with four players (two of whom were Frank Howard and Pete Richert) going to the Senators. As a Dodger, Osteen was finally made into a full-time starter. In his time with Cincinnati, he went 0-1; in his time with the Senators, he went 33-28. As a Dodger, his career finally took off.
After two years with an earned run average under 3.00, Osteen was considered a top starter and a workhorse. In those two years, Osteen and the Dodgers had reached two straight World Series, the last two Osteen would reach in his career. In the 1965 World Series, the Dodgers would beat the Minnesota Twins in 7 games, and Osteen pitched brilliantly. He had a 0.64 ERA in the Series with a 1-1 record including a shutout, which came after teammates Don Drysdale and Sandy Koufax lost their respective games, the first two games of the Series. In the 1966 World Series, the Dodgers would lose to the Baltimore Orioles in 4 games. Osteen gave up only three hits in seven innings in Game Three, only to lose 1-0, his efforts outdone by Wally Bunker's six-hit pitching; a home run by Paul Blair accounted for the game's only run. Osteen's final postseason statistics include a 0.86 ERA with 7 strikeouts in 21 innings pitched.
In , he reached his first All-Star game, going 17-17 with a 3.22 ERA in 288⅓ innings pitched. He also picked up 14 complete games on the year, with 5 shutouts. In , Osteen won 20 games for the first time and set a number of career highs:
Moving towards the 1970s, Osteen was still pitching an amazing average of 260 innings a year, which made people often consider him a link to old-time baseball.
In , Osteen pitched three shutout innings in the all-star game and got the win, a game remembered most by Pete Rose's barreling into Ray Fosse to score the winning run in the 12th inning. Coincidentally, like Osteen, the pitcher and hitter involved in the walkoff single were also Tennessee natives: Jim Hickman (a Dodger teammate of Osteen's in ) collected the hit off losing pitcher Clyde Wright.
In , Osteen had an incredibly strong year finishing with 7 complete game victories in his last 9 starts. That year, he was 20-11 with a 2.64 ERA in 252 innings pitched.
He made his 3rd and final All-Star team in , in his last real quality season, and his last season with the Dodgers. That year, he went 16-11 and had a 3.31 ERA with a 2nd-place Dodger team. In his 33 starts on the season, he had 12 complete games and 3 shutouts. He had won in double figures each year from 1964-1973.
Osteen played his final game on September 27, with the White Sox. He was released by them on April 5 of the next year.
Osteen's career statistics included a 196-195 record, a 3.30 ERA, 1612 strikeouts, and 140 complete games (40 shutouts) in 3460⅓ innings pitched and 541 games. He hit 45 batters and threw 67 wild pitches.
As a batter, Osteen had a .188 batting average with 8 home runs and 76 runs batted in.
He later became a pitching coach for the Cardinals, Philadelphia Phillies, Texas Rangers and the Dodgers as well as various minor league teams.


