Oswalt had another rough showing as the San Diego Padres scored four tims in the seventh inning Sunday, boosted by pinch-hitter Nick Hundley's three-run double, for a 5-2 win over the Colorado Rockies.
"The bad thing about it is, I'm running out of time to get arm strength back," said Oswalt, whose ERA rose to 8.57. "I haven't had a lot of luck go my way."
San Diego swept the three-game series with late-inning victories in all three.
After Oswalt (0-5) walked home the tying run in the seventh, Hundley hit a sharp grounder down the third-base line off Wilton Lopez to clear the bases.
Oswalt allowed five runs on four hits with two walks in 3 1-3 innings in relief of starter Chad Bettis.
"I wanted to try and keep it down velocity-wise," Oswalt said. "I felt OK."
The 36-year-old Oswalt had been on the disabled list with a left hamstring strain for two months before being activated on Friday. The former 20-game winner was 0-4 with a 7.64 ERA in four starts this season with Colorado.
The Padres loaded the bases against Oswalt in the seventh on a leadoff walk to Chase Headley and consecutive singles by Kyle Blanks and Ronny Cedeno.
After a short flyout, Oswalt walked pinch-hitter Guzman on four pitches to force in a run and tie it at 2. Lopez then relieved Oswalt to face Hundley.
Rockies manager Walt Weiss went to the mound before the walk to Guzman but decided to leave Oswalt in the game.
"He threw the ball really well," Weiss said. "I went out to talk to him and he said he felt real good. He said he felt strong. He said he was going to get the guy to hit into a double play, so I left him in there."
It was the first time since June 1998 that the Padres have won three straight games despite being tied or behind in the seventh inning or later in each of the three games.
Nick Vincent (4-2) pitched one inning for the win. Huston Street worked the ninth for his 29th save in 30 chances.
The Rockies took a 1-0 lead in the third when Corey Dickerson tripled and Michael Cuddyer doubled.
Colorado added to its lead after Charlie Blackmon reached on a one-out error by shortstop Ronny Cedeno in the fourth and Jordan Pacheco followed with a run-scoring double.
Renee Rivera's sacrifice fly cut the lead to 2-1 in the fifth inning.
NOTES: The Padres swept Colorado at home for the first time since September 2006. ... Rockies C Wilin Rosario was not available because of issues with his wisdom teeth. ... Rockies CF Dexter Fowler (right knee strain) missed his second straight game. ... Despite being swept, Colorado won the season series against San Diego 12-7. ... The Rockies play at San Francisco on Monday night when RHP Jhoulys Chacin (13-8, 3.16 ERA) opposes RHP Tim Lincecum (9-13. 4.50). ... The Padres travel to Philadelphia and will open with RHP Andrew Cashner (8-8, 3.45) against RHP Tyler Cloyd (2-3, 3.57) on Monday night.