"I felt it in the first inning, on my slider," Oswalt said of the injury, which he believes isn't serious. "It kind of bit me a little bit, but I was just trying to eat up a few innings after that."
But with the way B.J. Upton was swinging the bat, it didn't matter who the Rangers had on the mound. Upton tied a Rays record with three home runs, all solo shots.
"You have to tip your hat to B.J. Upton," Washington said. "Even if they don't get those other runs, they still beat us three to nothing."
Texas' offense, meanwhile, didn't do its pitchers any favors. The Rangers were held scoreless on Sunday and put up just five runs in the three-game series.
"If you look at the game today, you have to give credit to James Shields," Washington said. "When a guy is pitching like that, it makes you look like you're lethargic."
The Rangers had just three baserunners against Shields. Elvis Andrus reached in the first because of an error by first baseman Carlos Pena. Nelson Cruz reached an inning later when Pena couldn't handle a throw from shortstop Ben Zobrist, though the play was ruled a hit.
It wasn't until the eighth inning that Texas finally got its first clean hit, a single up the middle by David Murphy. Shields retired 19 straight Rangers leading up to that point.
"He had a tremendous changeup," Washington said. "He certainly didn't waste a whole lot of pitches. We just couldn't find the fat of the bat. You just have to tip your hat."
Shields ended the day with a complete-game shutout, allowing just two hits to go with eight strikeouts.
"Obviously, September baseball is huge, and getting any kind of win is big," Shields said. "But against that lineup ... As far as I'm concerned, that's the best hitting lineup in the big leagues, one through nine. Not to mention they have a lot of guys on the bench who can swing it, too. That's a good hitting team over there. They can do some damage any time."
With the loss, Texas dropped two of three to Tampa Bay and saw its lead over Oakland in the American League West shrink to four games, pending the A's outcome in Seattle.
"We're playing well. Today wasn't our day," Michael Young said. "We battled hard over the last three or four games. Today definitely wasn't our day, but we've been battling hard, playing hard."
Upton drilled Oswalt's first pitch of the day over the fence, his 19th dinger of the season. It was the first time a Texas pitcher gave up a homer on the first pitch since May 16, 2007, when Elijah Dukes took Vicente Padilla deep, also at Tropicana Field.
Later in the frame, Matt Joyce hit a two-out double with two runners on that scored Zobrist from second, doubling Tampa Bay's lead. The Rays couldn't extend it further, though, when Ryan Roberts grounded out to short.
Oswalt's troubles continued in the bottom of the second. Pena, who entered the game batting just .189, hit an opposite-field single against an aggressive shift. Jose Molina, who entered with a .205 average, followed with another long ball to push Tampa Bay's lead to four runs.
Martin Perez came in to relieve Oswalt after the second, but Upton didn't skip a beat. Upton in the fourth drilled a 3-0 fastball to left field for another bomb, giving him his fourth career multihomer game and second this season.
Upton came back to the dish in the sixth and sent another Perez offering over the left-field fence for his final homer of the afternoon.
"I don't know, man, I can't really put it into words," Upton said of his big game. "You kind of dream about doing things like that, and it doesn't happen very often. For me to come out and do it today to help this team against a good Texas ballclub, a team that pitches well, too, it feels really good."
The two long balls he gave up to Upton aside, Perez pitched relatively well, not allowing any other runs. He gave up seven hits and a walk over five innings, with three strikeouts.
"He did a great job, especially after Roy came out of the ballgame," Washington said. "He gave us five innings of two-run ball, and both [runs were] off of B.J. Upton, who had one heck of a day today."