Thomson pitched seven innings and Shane Spencer homered as the Rangers took advantage of three Detroit errors in a 6-3 victory over the Tigers on Thursday night.
Thomson (10-10) started Monday against Detroit but threw only 20 pitches before a rain delay of almost two hours. He was pulled when his arm stiffened during the delay, and Showalter decided to bring him back three days later.
The short layoff didn't seem to hurt.
Thomson, who went to the bullpen to warm up a little earlier than normal to loosen up a stiff back, allowed three runs and nine hits in winning for the sixth time in seven decisions. He struck out six and didn't walk a batter.
"It took a little longer to get loose before the game, but I was fine after the first inning," Thomson said. "I always go out there and try to find a rhythm, and the execution of my pitches was a little better tonight."
Showalter's confidence was rewarded as Thomson pitched at least seven innings for the 12th time this season, keeping the Rangers in the game despite only average command of his pitches.
"You're not always going to go out with your best stuff," Showalter said. "That's what separates you as a starting pitcher."
Thomson was excited to reach 10 victories for the first time in his pro career. He is the first Texas pitcher to reach double-digit wins this season.
"I thought I could be a pitcher who could win 15 games," Thomson said. "It's nice to have a shot at it."
Francisco Cordero pitched a perfect ninth for his 10th save in 17 opportunities.
Warren Morris went 3-for-4 with two RBI for the Tigers, who have lost 21 of 27 since the All-Star break and own baseball's worst record -- 31-87.
Spencer led off the second with his 10th homer of the year, and the Rangers got more help from the Tigers' shoddy defense. Nivar bunted for a base hit, and Todd Greene scored when pitcher Matt Roney's throw to first hit Nivar in the leg.
The Rangers chased Roney (1-8) in the third, loading the bases with no outs. Nix then hit a two-run single off Shane Loux, making it 5-1.
"We've done a good job taking advantage of our opportunities," Nix said. "We have a lot of confidence in our approach with guys on base. We've been patient and looking for good pitches to hit."
Roney allowed five runs and five hits over two-plus innings.
Tigers manager Alan Trammell said Roney could be headed for the bullpen. That decision will be made Friday, Trammell said, with Loux the probable replacement for Roney.
"He hasn't been very good for quite a while," Trammell said. "I'm thinking about making a change. We have to do better than that."
Roney fell behind with several hitters, and he paid for it.
"I couldn't locate my pitches early," Roney said. "I fell behind, and I can't pitch like that."
The Rangers weren't done taking advantage of the Tigers' errors. Nivar beat out an infield single against Loux in the fourth, going to second on third baseman Shane Halter's throwing error. He scored from third on Alex Rodriguez's single.
Detroit got two runs in the fifth with the help of a throwing error by Greene, the catcher. Ramon Santiago was on third and Sanchez on first with two outs. Sanchez stole second, and Santiago scored on Greene's wild throw. Sanchez crossed the plate when Morris doubled, making it 6-3.
Trammell said he was embarrassed by his team's sloppy performance.
"I'm not happy with the way we played," Trammell said. "I take it as a personal reflection. I know people will look at this game and say we're the worst team in baseball. When we play like this, it bothers me."
The Rangers' third out in the second inning came on batter's interference. Nivar apparently had stolen second, but plate umpire Wally Bell ruled that Blalock's swing interfered with catcher Brandon Inge's attempt to throw out Nivar, and Blalock was called out. ... Texas Gov. Rick Perry threw out the ceremonial first pitch. ... The Tigers have been outscored 93-45 in the first inning.