There's a reason Mike Napoli was so appealing to the Red Sox.

After last season, the Sox made Napoli -- a career .259 hitter who entered this season with a .306 average, 7 home runs, 17 RBI, a .397 on-base percentage, and .710 slugging percentage in 19 career games at Fenway Park -- one of their prime free-agent targets. His right-handed power and natural pull swing were made for Boston, and, after an initial deal was scuttled by a medical issue with his hip, the sides reached a one-year agreement that dropped Napoli into the middle of the Red Sox batting order.

And the Sox have gotten their payoff.

Napoli blasted a grand-slam home run into the Monster Seats in left-center in the fifth inning Monday night, the big blow in the Red Sox' 9-6 win over the A's. It was part of a 2-for-4, 5-RBI night that lifted his average at Fenway this year to .305 (11-for-36) with 5 doubles, 2 home runs, 12 RBI, 6 runs scored and a .611 slugging percentage. Overall he's hitting .278 and leads the American League in RBI with 25.

"That's what we were hoping he'd be able to do," said manager John Farrell.

“I love hitting here," Napoli said. "You got the wall right there and you can get away with some stuff. You don’t necessarily have to hit it so good. Sometimes you hit a pop fly that would be an out in another park, but it goes off the wall. So it’s definitely fun hitting here and I enjoy it.”

Especially enjoyable was Monday night's grand slam, the fourth of his career and his first since July 8, 2011, against the A’s while with the Rangers.

“It was an exciting moment,” Napoli said. “I was down, 0-1. I was just trying to drive something, get a sac fly, just put a ball in the air out there. And I just got a pitch to drive and I hit a grand slam.”