"It was just one of those days," said Fielder, who had one of the Rangers' three errors and a base-running mistake that took Texas out of a possible big inning. "Everyone played hard, we made mistakes here and there. It just didn't go our way. It's nothing that you can't really see. We've just got to come back tomorrow and fix it."
Saunders (0-1) left in the fourth inning with a bruised left ankle after getting hit by Evan Longoria's liner. Saunders gave up five runs and six hits, including a three-run home run to Sean Rodriguez, in 3 2/3 innings.
"I think I was trying to be too fine early in the game," Saunders said. "The pitch to Rodriguez was a decent pitch; he just put a good swing on it. Probably the wrong pitch at the wrong time."
Rodriguez tied a career-high with four RBIs and Jake Odorizzi got his first major league win for the Rays (3-2).
Rodriguez was back in the lineup after missing Thursday night's 7-2 win over Toronto for the birth of his son.
Odorizzi (1-0) allowed three hits in six innings in his seventh big league start and 10th game overall. Ryan Hanigan hit a three-run homer during the fifth for the Rays.
Fielder got his first RBI since Sept. 22, a drought of 20 regular and postseason games, with a run-scoring single in the eighth. But the Rangers (2-2) wasted a great scoring opportunity in the fourth, when they were down 4-0.
With runners on first and second and one out, Mitch Moreland singled into the right-field corner, but Fielder got tagged out in a rundown between third and home.
"Prince just blew it. He just messed up. That's all you can say about it," said manager Ron Washington.
"I just didn't get a good jump," Fielder said. "It was my fault."
"It was obvious during training that every time we made a mistake it cost us," Washington said. "We certainly have to tighten down our defense. We don't have a pitching staff that strikes people out right now and we certainly can't have them getting four outs an inning. So that certainly has to get better, and it will."
Tampa Bay manager Joe Maddon won his first replay reversal in the seventh after it was first ruled that right fielder Wil Myers didn't make the catch while sliding forward on J.P. Arencibia's two-out flare. After a 1-minute, 43-second delay, the umpires changed the call to an out.
Texas RHP Nick Martinez will make his major league debut in Saturday night's game against the Rays. "Go out there and relax, and use his pitches," Rangers manager Ron Washington said. "Get us as many outs as you can. Be out there as long as you can. Believing in himself, believing in the stuff he has, and using it." ... LHP David Price will start Saturday for the Rays. ... Rangers LHP Matt Harrison (back) will make his next minor league start Tuesday. He went two innings in a rain-shortened outing Thursday for Double-A Frisco. ... Tampa Bay sent RHP Juan Carlos Oviedo (elbow ligament replacement surgery) to Triple-A Durham on a rehab assignment.