The All-Star right-hander knows when to use his best pitch.
Shields tossed a four-hitter for his major league-best 11th complete game and the Rays beat the AL West-leading Texas Rangers 5-1 on Monday.
"He's got a good changeup, period," Rangers slugger Josh Hamilton said. "So, when you've got a good changeup, 90 (mph) looks more like 96. He looks so good to hit, and it drops off the table. He throws it and keeps it out of the strike zone. Makes it look like it's going to be in the strike zone."
Shields (14-10) struck out six and walked two. The only run he allowed came home on Michael Young's grounder with one out in the ninth.
"Whether they're stressful innings or not, I condition myself enough to go that deep into games," Shields said.
Shields also became the first AL pitcher since Randy Johnson in 1993 to have at least 200 strikeouts and 10 complete games in the same season when he fanned Hamilton in the first.
The only other 200-strikeout, 10-complete game pitcher since 2000 was CC Sabathia, who accomplished the feat when he pitched for Cleveland and Milwaukee during the 2008 season.
"This year, the guy's been able to finish whatever he starts," Texas manager Ron Washington said. "We haven't been able to figure him out."
Shields went eight shutout innings in Tampa Bay's 4-1 win at Texas last Wednesday. The right-hander is the first AL pitcher since Scott Erickson in 1998 to record at least 11 complete games.
"He's growing into this moment and he's pretty much in his sweet spot as a starting pitcher goes," Tampa Bay manager Joe Maddon said. "I think it's important to him to build his confidence and let him become one of the premier starting pitchers in baseball. I don't want to get in the way of that, either.
"It's a fine line you walk, and with a guy like him, his workout ability and his ability to take care of himself permits you to let that occur."
Texas starter Scott Feldman (1-1) gave up four runs and four hits in five innings. The Rangers were coming off a big series at Boston during which they won two of three.
Longoria hit a solo drive in the first for his 25th homer. He has 61 RBIs over his last 67 games.
Casey Kotchman drove in two with a single and another run scored on John Jaso's double-play grounder as Tampa Bay went up 4-0 in the fourth. The Rays loaded the bases with one out on three walks from Feldman.
Upton added a solo shot in the seventh.
Feldman made his second spot start this season in place of Alexi Ogando, who the Rangers thought needed a break. The right-hander threw six innings in his other start, a 2-0 win over Tampa Bay last Tuesday.
Ogando entered in the eighth and gave up a double during a scoreless inning.
Washington said it has not been determined if Ogando, who is 12-7 this season, will pitch again out of the bullpen before making his next start.
Texas had a runner on second with two out in the first, second and fifth, but failed to score. Shields induced a double-play grounder from Young after Hamilton drew a walk to start the fourth.
The Rays have won 17 games in a row when scoring five or more runs. ... Tampa Bay DH Johnny Damon (sore leg) rested. ... Texas 3B Adrian Beltre, who returned from a strained left hamstring last Thursday, is scheduled to DH twice in the three-game series on artificial turf. ... Rays 2B Ben Zobrist was back in the lineup after missing two games because of neck stiffness. ... Washington said the left index finger of LHP C.J. Wilson (14-6), Tuesday's scheduled starter, is fine. Wilson had an infield single in his start last Thursday go off the finger. ... Maddon said C Kelly Shoppach will come off the bench as the team takes a close look at other catchers, including Jose Labaton. ... Rays RHP Jeff Niemann (9-6) will pitch against Wilson on Tuesday.