SEATTLE - Jason Vargas has a long history of having second-half struggles.

Until now. Vargas continued his impressive second half with seven strong innings against the Boston Red Sox as the Seattle left-hander improved to 14-9 and helped the Mariners to a 4-1 win on Monday that sent Boston to its seventh straight loss.

In his first three seasons with Seattle, Vargas was a composite 7-18 after the All-Star break, but this season he's turned it around. He's 6-2 since the break this year.

``The last few years I've struggled after the All-Star break,'' Vargas admitted. ``So to be able to make the adjustment I needed to not struggle is definitely a plus.

``It shows that I'm able to make the adjustments I need to make, and then keep making them.''

Vargas, just the third Seattle pitcher since 2003 to record 14 or more wins in a season, is a major reason the Mariners have the second-best record in the American League since the All-Star break at 30-19, including a 19-7 record at Safeco Field. Vargas has three of his second-half wins in Safeco.

``Jason has made some adjustment that he's been able to bring into this year,'' manager Eric Wedge said. ``He's really worked hard to be strong here in the second half, really worked hard between starts.''

He got all the help he needed in a four-run fourth inning when John Jaso and Jason Smoak delivered RBI singles off Boston starter Clay Buchholz and the Red Sox contributed two errors to the inning.

Seattle's second-half surge has pushed the Mariners (66-70) to just four games under .500 after they were 16 games under .500 on July 14. The best Seattle has been since the break is three games under at 61-64.

It's been a totally different story for the Red Sox, whose seven-game losing streak is the longest for the organization since the last month of the 2001 season.

Club owner John Henry and general manager Ben Cherington, neither of whom generally is on the road with the club, were both on hand Monday. Cherington said, for him, it was a pre-planned trip that had nothing specific to do with the losing streak. He said that Henry was already on the West Coast on other business.

That being said, the Red Sox are not used to losing like this; they've been outscored 58-16 in the seven games, losing by an average of six runs per game.

``Its' hard to watch,'' Cherington said. ``But the only choice we have today is to show up the next day and play.''

Buchholz shut the Mariners out for six of the seven innings he pitched. But four of the six hits he allowed came in the fourth inning, as did two Boston errors that helped prolong the inning.

``It's tough to deal with it, but it's a game,'' he said. ``Playing in Boston can take a toll on you. But we've got to find a way tomorrow.''

Boston manager Bobby Valentine tried to take this one in stride.

``Clay did what he had to do and gave us a chance to get the lead, and we just couldn't do it,'' Valentine said. ``I think the team is very mentally and physically tired. We need the night off here to come back; it will feel like two nights.''

Boston got a first-inning run on Dustin Pedroia's 1000th career hit, a double, and a Cody Ross single in the first inning. Boston hitters went 0-for-5 with men in scoring position from that point on. The Red Sox are 12 games under .500, a season low.

Pedroia finished with two hits and has a 14-game hitting streak.

``Dustin's really doing great,'' Valentine said. ``Everyone else has got to follow suit.''