The Tampa Bay rookie allowed four hits in seven innings and became the first Devil Rays pitcher to begin his career with four straight victories by beating the slumping Diamondbacks 3-2 on Wednesday night.
"He's nasty. What he does is he changes speed," catcher Toby Hall said of the 24-year-old right-hander. "He has one of the nastiest changeups in the league that I ever caught or faced. Johan Santana is the other one."
The Diamondbacks did their homework on Shields (4-0), but still weren't fully prepared.
"We knew going in he was going to throw a bunch of changeups. We just couldn't stay back on them," Arizona manager Bob Melvin said.
"It's one thing to say you're going to sit there and try and hit it; it's another thing to stay back on it when you're taught to hit the fastball. ... He threw just enough fastballs to get us off the changeup."
Shields held the Diamondbacks hitless until the fifth inning and finished with five strikeouts and three walks.
Meanwhile, Rocco Baldelli continued his torrid hitting with a run-scoring single for the Devil Rays, who improved to 7-1 against NL opponents after going 3-15 in interleague play a year ago.
Baldelli, who missed all of 2005 and the first two months of this season with a variety of injuries, went 2-for-3 against Brandon Webb (8-3) and is hitting .388 with two homers and six RBI in 13 games since coming off the disabled list.
Arizona lost for the 14th time in 16 games and remained the only team that's never beaten the Devil Rays. The Diamondbacks are at .500 (36-36) for the first time since they were 13-13 on May 1. They were 34-22 on June 4 before beginning their current slide.
Tampa Bay has won seven of 11.
"It feels good," Shields said. "I came here to help this team win some games. Hopefully I can keep going. ... There's a good atmosphere in the clubhouse right now."
Shawn Camp pitched the eighth for Tampa Bay and Brian Meadows worked the ninth for his first save of the season.
Webb, who allowed three runs and eight hits in six innings, dropped his third straight decision after winning eight in a row to begin the season. He hasn't won since beating Cincinnati 3-0 on May 26, a span of five starts.
"I don't think he pitched poorly enough to deserve a loss," said Melvin, who was ejected during the fifth inning for arguing balls and strikes. "We just offensively couldn't figure the other guy out."
The Devil Rays scored twice in the second, despite not getting a solid hit off Webb.
Russell Branyan's routine fly dropped for a double when left fielder Luis Gonzalez lost the ball in the lights and domed ceiling, then Jonny Gomes reached on a grounder to third that hit the bag and bounded into the air for a single.
"I just lost it early," Gonzalez said. "I haven't played a lot of games here. ... I just lost it. I'm sure I'm not the first guy that's done it here. It just came at a crucial time for us."
Branyan took third on Gomes' hit and scored on a balk. Hall followed with a soft liner that barely cleared the infield and rolled into foul territory along the third base line for a run-scoring double.
Baldelli's RBI double in the third made it 3-0.
Although Shields held the Diamondbacks hitless until the fifth, the 24-year-old right-hander was far from perfect in the first four innings. Besides hitting batters in the first and fourth, he walked two in the third.
Once the Diamondbacks broke through, though, they closed the deficit in a hurry. Orlando Hudson doubled four pitches after Jeff DaVanon got the first hit off Shields, driving in Arizona's first run. Eric Byrnes doubled one later, making it 3-2.
Melvin's ejection was his first this season and 13th of his career. ... Webb struck out five and walked a season-high four. ... Tampa Bay has won all five meetings between the expansion clubs, which both began play in 1998. ... The Diamondbacks placed LHP Terry Mulholland and RHP Russ Ortiz on unconditional waivers. OF Scott Hairston was placed on the 15-day DL with a right shoulder injury and RHP Casey Daigle was recalled from Triple-A Tucson. ... The Devil Rays signed INF Jason Romano to a minor league contract. He's expected to join Triple-A Durham on Thursday.