The Oakland Athletics may own the best record in the majors, but the Kansas City Royals have won 17 of their last 21 - including four of the six meetings this season. The Royals look to continue their quest for their first postseason appearance since 1985 when they conclude their four-game series versus the visiting Athletics on Thursday. Omar Infante belted a two-run homer in Wednesday's 3-0 triumph and is 6-for-15 with four RBIs in his last four games versus Oakland.While Kansas City clings to a half-game lead over Detroit in the American League Central, the Athletics saw their advantage over the second-place Los Angeles Angels dip to 2 1/2 in the AL West. Josh Donaldson followed his two-homer performance in Tuesday's 11-3 triumph with a double to extend his hitting streak to 10 games. Donaldson is 5-for-10 with four RBIs in this series after going 1-for-10 when Kansas City claimed two of three from Aug. 1-3.TV: 2:10 p.m. ET, MLB NetworkPITCHING MATCHUP: Athletics RH Jeff Samardzija (5-8, 2.91 ERA) vs. Royals RH James Shields (11-6, 3.25)Samardzija improved to 3-1 since being acquired from the Chicago Cubs after allowing two runs in six innings in a 9-4 victory over Minnesota on Saturday. The 29-year-old has worked at least 6 2/3 frames in each of his seven starts with the Athletics, although he has yielded six homers with his new team. Former Milwaukee player Nori Aoki has enjoyed success versus Samardzija from their days in the National League, going 7-for-16 (.438) against him.Shields collected his second straight win in impressive fashion Saturday, scattering four hits to secure his first complete game and shutout of the season in a 5-0 victory over San Francisco. The 32-year-old improved to 6-4 in his career versus Oakland after permitting two runs on four hits in eight innings in a 4-2 win Aug. 3. Shields allowed two homers against the Athletics after yielding the same total in his previous seven contests.WALK-OFFS1. Kansas City 1B Billy Butler is 15-for-39 with two homers and seven RBIs during his last nine games.2. Oakland SS Jed Lowrie had a single Wednesday and is playing despite a hairline fracture on the top of his right index finger.3. Royals 1B Eric Hosmer is scheduled to have an X-ray Thursday to assess the broken bone in his right hand.PREDICTION: Athletics 4, Royals 1