The teams were holding off on an announcement until they were sure all players had been contacted. The teams completed negotiations in advance of Monday's 10 p.m. MT deadline for acquiring a player and having him eligible for a postseason roster.
Contreras has struggled to a 5-13 record with a 5.42 ERA in 2009. Contreras, a veteran of several pennant races with the Yankees and the White Sox, gives the Rockies an experienced starter heading into the final stretch. The Rockies and Giants are tied for the National League Wild Card.
A former star in Cuba before defecting, Contreras has appeared in two postseasons, with the Yankees in 2003 and the White Sox in '05. He is 3-3 with a 3.77 ERA in 12 appearances, including four starts, in the postseason.
Contreras started for the White Sox in Game 1 of the 2005 World Series against the Astros and Roger Clemens and won, 5-3. He went seven innings and gave up six hits and three earned runs. In '03 with the Yankees, he made four relief appearances in the Fall Classic against the Marlins and went 0-1 with a 5.68 ERA.
The Rockies could use a starter as soon as Saturday against the D-backs. That's when they need to fill in for right-hander Aaron Cook, who is out with a sore throwing shoulder.
The Rockies hope Cook, who suffered the injury on Aug. 21 in a game against the Giants, will return at some point before the regular season ends.
All three teams at the top of the NL West added pitching reinforcements. The Dodgers acquired Jon Garland from the D-backs, and the Giants announced they have signed Brad Penny, who was recently released by the Red Sox. The Dodgers also acquired slugger Jim Thome from the White Sox.
Hynick, an eighth-round Rockies selection in 2006, went 10-9 with a 3.83 ERA for Triple-A Colorado Springs.
Thomas Harding is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.