Any question as to how the Mariners have managed to get off to a surprising 5-2 start going into Tuesday's home opener can easily be traced to one significant item.

One week into the season, Seattle has the lowest earned run average in the American League at 2.92, a huge drop from last year's 4.73 ERA.

Yeah, it's early and all, but any time you're holding foes to under three runs a game, good things generally happen.

This isn't all about pitching, of course. The Mariners' defense has been excellent, particularly in the outfield with the addition of Franklin Gutierrez in center and veteran Endy Chavez in left or right.

Additionally, the Mariners currently lead the AL with sacrifices with four, two of those by Gutierrez.

"We've been able to do what some people call 'small ball,' but in my opinion is just fundamental baseball," said manager Don Wakamatsu. "The defense has been good. Our new acquisitions in the outfield have been really evident in helping save some of the ballgames."

That pitching-defense theory could be put to the test Tuesday when Carlos Silva takes the mound, given the veteran was the least-successful starter in Seattle's first trip through its rotation. Silva has a 10.80 ERA after surrendering eight hits, six runs and two long balls to Minnesota.

But the bullpen, expected to be a sore point for this club, has been lights out except for one Minnesota meltdown by closer Brandon Morrow.

"We had a tough spring (with the relievers)," Wakamatsu said. "We always said you don't judge on spring-training stats, but there was a lot that wasn't shown that these guys have shown me in the last week."

Wakamatsu said David Aardsma closed in Sunday's 1-0 victory at Oakland because Morrow had thrown 27 pitches the night before and the team is trying to be careful with him as he works his arm into shape.

Among the pleasant surprises are rookies Chris Jakubauskas and Shawn Kelley, who have contributed solidly to a bullpen that has a 2.37 ERA and a .154 batting average against in 19 innings.

Jakubauskas, 29, has been in the M's minor league system the past two years after pitching in the independent leagues. Kelley, 24, is a 13th-round draft pick who had never been above AA ball before now.

"Probably from the outside people were going, 'Wak is going with two complete rookies,'" Jakubauskas said. "Kelly and I want to make him look like a genius. I'm pretty sure there are some people who are skeptical, but we both know we can pitch. All we want to do is prove him right and help this ballclub win."

So far, so good.