Nix hit a drive off Manny Acosta (1-1) that barely cleared the wall in right-center field with one out for his first career game-ending homer.
Nick Masset (3-1) pitched the last two innings, giving up two singles in the 11th. Then, the Reds pulled out another one at the end—eight of their 13 wins have come in their final at-bat. They are 3-0 in extra innings.
Drew Stubbs also homered for the Reds, leading off the first inning with the first one allowed by Oliver Perez this season. Joey Votto had an RBI single off the left-hander, who lasted six innings and remained winless in six starts since Aug. 18.
In Philadelphia, Jaime Garcia allowed one run in six innings, David Freesehad three RBIs and Nick Stavinoha homered for St. Louis.
Garcia (3-1), a rookie left-hander, gave up three hits and struck out six.
Stavinoha delivered a pinch-hit homer leading off the seventh against Joe Blanton (0-1) and Freese added a bases-loaded double.
Jayson Werth hit a solo shot for the Phillies and has reached base in all 25 games this season.
Kyle McClellan yielded one run in two innings of relief for the Cardinals. Trever Miller allowed Chase Utley’ssolo homer in the ninth to make it 6-3 and Ryan Franklin recorded the last two outs.
Blanton, who was making his first start of the season, was on the disabled list while recovering from an oblique strain in spring training.
The Cardinals had 14 hits—10 against Blanton.
In Houston, Cesar Valdez won his major league debut and Chris Snyder hit a three-run homer to lead Arizona.
Chris Young had three hits and drove in three runs for the Diamondbacks, who snapped a three-game losing streak and sent Houston to its seventh straight defeat.
Valdez (1-0) was called up from Triple-A Reno on Monday and allowed one run in five innings. He gave up five hits and walked three.
Snyder’s two-out shot in the fourth gave Arizona a 4-1 lead.
Houston starter Felipe Paulino (0-4) yielded five hits and four runs in six innings.
In San Diego, Ubaldo Jimenez struck out a career-high 13, became the first six-game winner in the majors this season and hit an RBI single to lead Colorado.
Jimenez (6-0) held San Diego to one run and four hits in seven innings. He was making his third start since throwing the first no-hitter in franchise history, at Atlanta on April 17. He walked two.
He retired the last nine batters he faced, striking out five of the final six. His ERA rose from a major league-leading 0.79 to 0.87, dropping him into a tie with Livan Hernandezof Washington.
Jimenez, Joe Beimel and Rafael Betancourt combined for a six-hitter.
The Padres were coming off three shutouts in four games against Milwaukee.
Jimenez got all the backing he needed in the second on Clint Barmes’two-run double.
San Diego’s Kevin Correia (4-2) had his four-game winning streak snapped. He allowed three runs and four hits in six-plus innings.