In 2004, Chacín led all minor leaguers with 18 wins, and was the 24th pitcher used by the Blue Jays, tying the team record set in the 2002 season.

He was 16–2 with 109 strikeouts and a 2.86 ERA in 141+2⁄3 innings, having earned his promotion to the Syracuse Chiefs of the Triple–A International League after a 34-innings scoreless streak.

Chacín allowed two earned runs on three hits over seven innings for the win, as Toronto beat the Yankees 6–3.

At the end of the season, he had compiled a 1–1 record with six strikeouts and a 2.57 ERA in 14 innings At spring training in 2005, Chacín landed a spot in the Jays' starting rotation.

He finished the 2008 campaign at Dunedin with a 1-7 won-loss record, and a 7.88 ERA, and was granted free agency by the Blue Jays at the conclusion of the season.

Chacín signed a minor league contract with the Washington Nationals on December 23, 2008, but was released by that club at the conclusion of spring training.

Only a few days later, Chacín signed a minor league contract with the Philadelphia Phillies organization He split the 2009 season between the Lehigh Valley IronPigs, the Phillies' Triple–A affiliate, and the Double–A Reading Fightin Phils, compiling a cumulative 9–4 record and 3.20 ERA with 62 strikeouts across 106+2⁄3 innings pitched.

On May 3, 2010, the Astros purchased the contract of Chacin from the Triple–A Round Rock Express of the Pacific Coast League.

[10] He went 0–1 with the Bisons, compiling a 12.00 ERA in 15 innings of work, and was granted free agency after the season ended.