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ST. PETERSBURG, Fla. -- The streaking Tampa Bay Rays haven't missed a beat since losing Evan Longoria.

With their star third baseman sidelined for up to two months with a tear in his hamstring, the AL East leaders completed a four-game sweep of the Seattle Mariners on Thursday and own the best record in the major leagues at 18-8.

"We talked about getting off to a good start, and we got off the good start we needed," manager Joe Maddon said after a 4-3 victory over the Mariners extended Tampa Bay's winning streak to six. The Rays have won 11 of their past 12 games and hold the best mark in baseball for the first time since Sept. 28, 2010.

"Baltimore is playing well. Toronto is playing very good. The Yankees are fine, and the Red Sox are going to keep getting better," Maddon added. "We needed to get off to a good start to really make our mark in the division."

Longoria left after the third inning of the series opener. Elliot Johnson replaced him and delivered a game-winning RBI single in the 12th inning. Luke Scott and Sean Rodriguez had big hits during the series, and Thursday it was Jeff Keppinger's and Desmond Jennings' turns to step up.

Keppinger hit a two-run homer and added a two-run triple to back right-hander Jeff Niemann (2-3), who allowed three runs and seven hits over 5 2/3 innings. The bullpen didn't allow a hit the rest of the way.

"It was a great team effort," Maddon said. "Everybody played, everyone participated, everybody has a piece of the ownership right now, and I like that."

The Mariners concluded a 10-day, 10-game road trip with a season-high six-game losing streak. The skid came right after a four-game winning streak that included a sweep of Detroit to begin their three-city trip. Tampa Bay won three of the four games at Tropicana Field by one run, and took the other by two.

"Tough ballgames, tough losses," Seattle manager Eric Wedge said. "We're just not quite doing enough to finish off innings to take that lead back, especially on the road."

The Rays scored all of their runs in the second inning, with Keppinger and Jennings delivering the biggest hits of the day off Kevin Millwood (0-3).

Reliever Jake McGee retired all seven batters he faced, and Fernando Rodney worked a scoreless ninth inning for his ninth save in nine opportunities for Tampa Bay.

The inconsistent Mariners struck out eight times, hiking their total in the series to 46. They have been held to 12 runs during their skid.

Millwood retired the first two batters of the second inning before giving up an infield single to Will Rhymes and Keppinger's second home run of the season. The next two batters, Chris Gimenez and Rodriguez, singled and scored when Jennings tripled to right-center field for a 4-2 lead.

The Mariners got one of the runs back when Dustin Ackley doubled with one out in the fifth and scored on Ichiro Suzuki's double down the right-field line.

But Seattle continued to struggle with runners in scoring position, stranding the potential at second base in the fifth and sixth innings. John Jaso doubled leading off the sixth, but Niemann struck out Mike Carp and Justin Smoak.

Niemann departed after throwing 107 pitches. McGee fanned Michael Saunders to end the threat.

Game notes

Tampa Bay CF B.J. Upton sat out after leaving Wednesday night's game after the fifth inning because in his right quad muscle. The Rays don't think the injury is serious. Jennings shifted from left field to center field and Brandon Allen started in LF. ... The Mariners have lost eight straight games to Tampa Bay. ... Seattle flies home to open a weekend series Minnesota on Friday night. LHP Jason Vargas (3-2) gets the start against RHP Carl Pavano (1-2).