NEW YORK (AP) _ Everyone in pinstripes insists Mariano Rivera is still a safe bet, even after a rough start this season.

Perhaps he can prove it when the Red Sox return to town.

Boston usually presents the biggest challenge for the Yankees' star closer, and the AL East-leading Red Sox open a three-game series in New York on Monday night that could provide answers to some key questions about Rivera _ if he gets a rare chance to pitch.

Should his early struggles this year simply be attributed to sporadic work, or is he beginning to decline at age 37? Maybe the rival Red Sox have his number, a disheartening thought for Yankees fans in the midst of a miserable season thus far.

``The biggest nemesis so far for Mo has been we haven't had a chance to use him a lot,'' pitching coach Ron Guidry said. ``For guys like Mo, they have to throw every couple of days to stay sharp.''

With the Yankees scuffling in every way imaginable, their normally unflappable reliever hasn't had many late leads to protect as he tries to find his form in the last season of his contract.

Fourth on the career list with 416 saves, Rivera is 1-3 with a 6.75 ERA and only three saves in five opportunities after Sunday night's game against the New York Mets. He has pitched in just 16 of the club's first 42 games as New York has opened 19-23.

Most surprising, left-handers are batting a jaw-dropping .367 (11-for-30) against Rivera _ an unthinkable mark back when his vaunted cutter was boring in on their hands with a precise, sizzling hiss.

After more than a decade of dominance, his teammates say they're stunned whenever he fails.

``Every time, it's a surprise,'' Derek Jeter said. ``Mo is as consistent as they come. He's had rough periods, everyone's had rough periods. His attitude, his demeanour, his approach has never changed.''

But opposing hitters appear to be getting better swings against Rivera. He has given up three homers this year, the first two were go-ahead shots in the ninth inning. Seattle's Adrian Beltre hit one on May 7, and backup infielder Marco Scutaro of the Oakland Athletics connected on an 0-2 pitch on April 15.

Rivera allowed three homers all last season, two in 2005.

``I didn't see anything different. Sometimes you can make good pitches and still give up hits,'' Texas manager Ron Washington said after Rivera closed out a game against the Rangers this month.

Guidry and manager Joe Torre have made a concerted effort lately to get Rivera more regular work, putting him on the mound every three or four days regardless of the score.

Rivera thinks that has helped. He is 0-1 with a 2.57 ERA in seven games in May after going 1-2 with a 10.57 ERA in nine April appearances.

``I'm feeling much better,'' Rivera said. ``I'm throwing the ball better.''

The Red Sox were a big reason for his poor start. Rivera blew a save at Fenway Park on April 20 and was tagged for four runs and three hits by Boston a week later in the Bronx. He was used that night just to get some work in, but managed only one out and was lifted by Torre.

The next afternoon, Rivera preserved a 3-1 victory over the Red Sox for his first save. His only other saves this year came in a doubleheader at Texas on May 3.

``We definitely need to give him more chances,'' Yankees centre-fielder Johnny Damon said.

Boston hitters are 7-for-12 (.583) against Rivera this season, building on some of the uncommon success they've enjoyed during all those intra-division games over the years.

Rivera has a 3.19 ERA and 36 saves in 47 chances (77 per cent) during regular-season appearances vs. the Red Sox, who are batting .251 against him.

The right-hander has limited everyone else to a .210 average and compiled a 2.26 ERA while converting 89 per cent of his save opportunities, according to the Elias Sports Bureau.

``They just put the ball in play and they get a lot of cheap hits. That's what happened the last time, cheap hits,'' Guidry said.

Several key hitters in Boston's lineup have faced Rivera a lot, developing familiarity and perhaps a sound approach. Jason Varitek is 10-for-28 (.357) with a homer and eight RBIs against the New York closer, while David Ortiz is 7-for-18 (.389) with a homer and four RBIs.

Manny Ramirez has 35 at-bats against Rivera, though he's hitting only .200 with a homer and eight RBIs. Those are all just regular-season numbers, too. Rivera and the Yankees opposed the Red Sox three times in the playoffs between 1999 and 2004.

Boston fans relish the ninth-inning rally against Rivera when he failed to close out a sweep in the 2004 AL championship series, a comeback that sent the Red Sox toward the World Series title.

``They know what he's going to throw. They know what his ball is doing. That's the reason,'' Boston's Julio Lugo said. ``They go out there knowing that they're going to hit. They've hit him before and they're going to do it again.''

Rivera had 34 saves and a 1.80 ERA last season, when he was sidelined from Aug. 31 to Sept. 22 due to a muscle strain near his right elbow.

At the start of spring training this year, the soft-spoken pitcher made some noise by saying he was hoping for a contract extension. He warned the Yankees that if he becomes a free agent, he'll consider offers from other teams.

``Everybody has the same shot,'' Rivera said then. ``The Yankees will not have an advantage.''

General manager Brian Cashman told Rivera he'd rather wait until after the season to negotiate.

As for now, Jeter said he still gets the same feeling as always when the bullpen door swings open at Yankee Stadium and Rivera jogs in to Metallica's ``Enter Sandman.''

To Jeter, that means the game is over. Yankees win.

``Exact same feeling, every time, regardless of how things are going for him,'' Jeter said. ``And that feeling will never change.''