ST. PETERSBURG Rays SS Jason Bartlett left Saturday's game in the fourth inning with a right hamstring strain and is day to day. Bartlett said he thought the injury was mild. He's unlikely to play today and may get an MRI exam as a precaution. Bartlett had just raced to his left to try to field a ground ball up the middle by Carlos Quentin. The ball got by Bartlett, who grabbed his right hamstring and was attended to by the team's athletic training staff. Bartlett walked off on his own, with Sean Rodriguez coming in to play second and Reid Brignac moving to shortstop. Bartlett has started at short in 45 of the Rays' 50 games but has struggled at the plate (hitting .193 in May), which led manager Joe Maddon to move him from leadoff to the ninth spot against right-handers for the time being. Brignac can fill in at short if Bartlett is out for an extended period. MIXING IT UP: RHP Grant Balfour said that for a long time in his professional career, his slider was one of his best pitches. And Balfour said the fact he's incorporating the pitch more, and in better situations, has enabled him to get off to a strong start this season. Balfour boasts a 2.11 ERA with 21 strikeouts and three walks in 21 appearances. 'I always felt like I had a decent breaking ball; I just didn't really throw it,' he said. 'I felt like I just got into a rhythm with the fastball and felt like there was a year (2008) where I was getting it done, so I just stuck with it. 'Last year, I tried to maybe screw around with it too much. This year, I tried to get back to the basics.' Balfour went 5-4 with a 4.81 ERA in a career-high 73 appearances last season, giving up a career-high six homers. He has given up one this season and held right-handers to a .167 average. Maddon said a key to Balfour's rebound is that his velocity has gotten back to the mid 90s, and he's getting 'strike one.' 'He's gotten more to that aggressive, pounding the strike zone' pattern, Maddon said. 'He's getting ahead in counts. And then he's able to judiciously use his slider and has gotten some bad swings at that in the right moment. ' LEANING LEFT: There was another interesting lineup tweak, with C John Jaso at DH and switch-hitting Ben Zobrist out until he pinch-hit in the sixth. Maddon said with left-handed hitters faring better against White Sox LHP John Danks (.277 this season to .196 by righties), he wanted to stack as many lefties as possible. C Dioner Navarro, who entered Saturday 5-for-13 in his career against Danks, was behind the plate. Maddon acknowledged he would prefer to have a set lineup , but with a few new 'toys' such as Jaso and Hank Blalock and both CF B.J. Upton and 1B Carlos Pea struggling, it's about 'finding the right chemistry among the group.' MEDICAL MATTERS: Maddon said Matt Joyce (elbow strain) will stay with Class A Charlotte for the final eight days of his rehab assignment. The Rays talked about moving Joyce up a level, but the outfielder felt 'he was fine where he was in regard to seeing the ball' and 'doesn't need to see higher-level pitching.' Joyce is hitting .320 in eight games for the Stone Crabs. MISCELLANY: The Giants signed former Rays DH Pat Burrell to a minor-league deal; he'll join Triple-A Fresno. The Rays will hold their first broadcast auction today, with prizes that include a hitting lesson from 3B Evan Longoria. Pea and Balfour will sign autographs along the first-base line today from 12-12:30 p.m. The Stone Crabs' game in Dunedin on Saturday was postponed due to rain and will be made up in a doubleheader today starting at noon. Joe Smith can be reached at joesmithsptimes.com. 