BOSTON -- Complete mastery. That was Jon Lester not just on Sunday, but for pretty much the past three and a half months.

But as the season ticks into the final three weeks, Lester's dominance becomes all the more important. The lefty's latest power-pitching clinic was just about all the Red Sox needed to notch a 4-0 victory over the reeling Rays, capping a sweep of a day-night doubleheader.

Lester allowed just two hits over eight innings, walking three and striking out seven. He improved to 13-7 on the season while lowering his ERA to 3.29.

Meanwhile, the Rays, who were once in the same race for a postseason berth as the Red Sox, left town in the throes of an 11-game losing streak.

"It's been a long day of baseball but a good day of baseball," said Red Sox manager Terry Francona.

The Red Sox (84-58) seem to be coming together at the right time, with six wins in their past seven games. They stretched their American League Wild Card lead to four games as the Rangers split their twin bill against the Mariners.

"I think it's a testament to things finally getting settled," said Red Sox catcher Jason Varitek. "We've played better -- much better. We still need to pitch the ball well. That's a key. Our lineup's gotten longer and it's gotten better."

Then there is Lester, who has been as good as any pitcher in baseball during a torrid run that began on May 31. Over that 19-start stretch -- which has included 11 starts of one earned run or less -- Lester is 10-2 with a 2.02 ERA.

Not even a disruption in routine could impact Lester in this one. He threw 23 pitches Friday night in a game that was rained out during the top of the first inning. Two days later, he came out and fired a gem against Tampa Bay.

"I felt all right," said Lester. "It's not really your typical start but I felt like my body responded pretty well to the other day. I just tried to really focus on letting my body work today for me and getting in a rhythm and I was able to do that, for the most part."

The Red Sox now take the field with the expectation that they will win when Lester takes the ball. His 21 quality starts are three more than Beckett, the ace of the staff.

"That roll Josh was on is the roll that Lester is on now," said Red Sox left fielder Jason Bay. "The last three months or whatever, maybe even four months, I don't know, I think if you took out his first month or two, the stats, I don't know them, but I'm sure they'd be pretty good. I think it's kind of gone unnoticed because we didn't get him a lot of runs early on, so the won-loss record isn't as fancy as some other guys.

"He threw 30 pitches two days ago and went out and threw 100 more and gave up two hits. He's another guy that, for us, is throwing well at the right time."

Clay Buchholz, who fired seven dazzling innings while getting a no-decision in Boston's 3-1 victory in the early game, is another one of those guys. Meanwhile, Beckett has pitched well in his past two starts after a slump that lasted four outings.

"I haven't played on a team that's had this type of quality 1-2-3, and I mean, they can shut you down," said Red Sox reliever Billy Wagner, who pitched a scoreless ninth to close out the day. "They're electric when they're out there. What makes it even better is they're young, and when they step on the mound, they put their foot on the pedal and they roll."

Just don't expect Lester to boast about it.

"I was just trying not to do too much," Lester said. "I was trying not to grind myself to death out there. Some starts, that's been a problem for me."

All Lester needed was a little help from his offense. The Red Sox got one home in the bottom of the second, a rally started when J.D. Drew walked and David Ortiz ripped a one-out double to right. Mike Lowell's fielder's choice brought Drew in to make it 1-0.

Rays starter James Shields held the Red Sox until the sixth.

Drew again was the rally-starter, stroking a single to right. With two outs, Mike Lowell smashed a double into the corner. That put the slumping Jason Varitek in a big spot and the captain delivered, grounding a two-run single that handcuffed first baseman Willy Aybar and went into right field. Lester had a three-run cushion to work with.

"He took a nice swing," said Francona. "He hit that ball through him. That's a good swing at an important time of the game where we add on. It's nice to see him get rewarded."

Bay provided some insurance in the bottom of the eighth, looping a 302-foot homer just out of the reach of Rays right fielder Gabe Gross and on the fair side of the Pesky Pole.

It was home run No. 32 on the season for Bay, and easily his shortest.

"I had a really good view because I was running that way watching it, and I knew the wind was blowing that way and it kind of left my bat with a little bit of spin," said Bay. "I knew it had a chance. I almost missed first base because I didn't really know what was going on. I saw him jump, but I didn't know if it was foul or what was going on, and there was an emphatic home run call and everyone went crazy and that's when I knew."

In three games this weekend, Boston's starters gave up two earned runs over 20 innings.

"That's what you need this time of year is for those guys to step up and do their thing," Ortiz said.