BOSTON — More than anyone else on the Red Sox, Mike Lowell understands Josh Beckett.

The two played together for parts of three seasons as teammates with the Florida Marlins, then were shipped together to Boston in a huge seven-player trade in November of 2005.

So Lowell wasn’t surprised to see that, with more than three weeks remaining in the 2007 season, Beckett last night became the first pitch to win 17 games, establishing a career-high. (The Yankees Chien-Ming Wang beat Seattle a few minutes later to also get his 17th win.)

“I believe he has a better understanding of what hitters do with certain pitches,” said Lowell after Beckett limited the Toronto Blue Jays to three runs on five hits in a 5-3 victory. “There’s a learning curve that I don’t think people understand and Josh has made adjustments very well.”

Beckett’s lone mistake last night came in the fifth inning when he left a changeup up to Matt Stairs, who drove it into the bullpen for a three-run blast.

“Even there,” said Lowell, “I think he showed that he’s much more composed. He didn’t let that three-run homer rattle him. He’s got a golden arm and he has the ability to throw 95 (mph), even in the eighth inning.”

Beckett’s effort — followed by a perfect ninth inning from closer Jonathan Papelbon — couldn’t have been more welcome, as it stretched the Red Sox winning streak to four games and allowed most of the bullpen a night off after Monday’s four-hour marathon.

“He sure has been everything we ever hoped for,” said manager Terry Francona.

At a time of year when pitchers begin to wear down, Beckett has shown great durability. In 10 of his last 11 starts, he’s gone at least six innings. Moreover, over his last 13 starts, dating back to June 24, Beckett has averaged 9.2 strikeouts per nine innings. He fanned seven last night.

Despite the home run allowed to Stairs, Beckett has also greatly reduced the number of gopher balls he’s thrown this year. After allowing 30 homers in his first season with the Red Sox, he’s cut that number to just 12 with another four or so starts remaining.

“He knows the hitters,” said Lowell, “and he knows the game plan and he’s been able to excuse to a T.”

“He’s able to locate his fastball with downward movement,” said Francona, “and he’s got two off-speed pitches. If he locates his pitches where he wants, it’s hard to get a swing on them and drive them out of the ballpark.”

Beckett is positioned to win 20 and perhaps win the American League Cy Young Award, but those honors seemed unimportant to him last night.

“I’m just looking to get No. 18,” he said. “I’ve got to move on. I’ve got another (start) in five days.”

Beckett got plenty of support in the fourth when, with the Sox already leading 1-0, Jacoby Ellsbury hit his second major-league homer in the last three days, thus matching in 30 at-bats his homer total for 436 at-bats in Portland and Pawtucket.

Back-to-back doubles from Julio Lugo and Dustin Pedroia accounted for the fourth run of the inning.

But the big inning wouldn’t have happened unless Coco Crisp sprinted down the first-base line to stay out of a double play as J.D. Drew scored on a fielder’s choice. Crisp’s throw beat the relay to first by shortstop John McDonald by a half-step.

On the very next pitch, Ellsbury flexed his new-found power stroke and the Sox were ahead, 3-0.

“Everybody recognizes Coco’s quickness,” said Francona, “but his willingness to try to get down the line (was key). If he doesn’t, we don’t score in that inning and that allows us to have what happened, happen. (If Crisp wasn’t safe,) Ellsbury doesn’t even hit and Pedroia doesn’t come up. That was really big, obviously.”

Stair’s blast in the next inning pulled the Jays to within a run, but Beckett never wavered. He faced 10 more batters the rest of the way and allowed just one more hit — a leadoff single to Frank Thomas — which was quickly erased by a double-play.

The Sox wasted a two-out triple from Ellsbury in the sixth, but a booming shot into the front rows of the center-field bleachers by Kevin Youkilis extended the lead. It was Youkilis’ fourth homer in his last dozen games.

smcadam@projo.com