"When I was with the Yankees he had a good fastball and he threw it a lot," Matsui said through an interpreter. "He still has a good fastball but what stood out to me was his command and overall skill."
Harden, who was reinstated from the 60-day disabled list earlier in the day, allowed two runs and four hits in his first start for Oakland in three years. The oft-injured right-hander struck out six and walked none.
"I was excited to get back out there," said Harden, sporting the beginnings of a beard. "It's something to build on. I knew I had a limit but I never thought about it."
Ryan Sweeney, Coco Crisp and Cliff Pennington each drove in a run for the A's, who won for the third time in 10 games following a four-game winning streak. Crisp also robbed Gerardo Parra of a homer and Matsui swiped a bag for the first time since Sept. 12, 2007, for the Yankees at Toronto.
"He's smart and he did it on his own," A's manager Bob Melvin said of Matsui's steal. "That was big for us. It got us on the board and got us going."
"They got big hits and we didn't, especially early," Johnson said. "We have to be ready from pitch one. It seems like the last couple games it's been kind of sluggish to start."
Arizona starter Josh Collmenter (4-5) lasted just 4 2/3 innings, yielding five runs and seven hits. The rookie right-hander is 0-4 with a 7.54 ERA in his last four outings and hasn't won since he beat Washington on June 3.
"It's been a pattern actually," Arizona manager Kirk Gibson said. "He's got to mix things up a little bit. I'd like to see him use his breaking stuff more. We came out flat again, and there's really no excuse for that."
Andrew Bailey worked the ninth for his seventh save in eight chances.
Pena's two-out homer in the second gave the Diamondbacks a 1-0 lead. It was his fourth of the season in a span of 10 games. He hit two in 64 games for the Washington Nationals in 2008, the last time he was in the majors.
Matsui walked, stole second and scored on Sweeney's two-out single in the fourth, and Oakland chased Collmenter with three consecutive two-out RBI hits in the fifth. David DeJesus and Scott Sizemore each singled with one out. After Jemile Weeks flew out, Pennington and Crisp each singled home a run and Matsui doubled home two more.
"It was Rich's first start and you could sense something different in the dugout," Matsui said. "It's nice to see that kind of potential. It gives us something to look forward to in the second half."
Stephen Drew singled in a run in the sixth for Arizona, and Johnson's two-run shot cut it to 5-4 in the eighth. But the Diamondbacks' rally fizzled.
Crisp took a home run away from Parra leading off the sixth. He reached over the fence to pull in the 400-foot fly, and Parra responded by tipping his helmet toward the center fielder.
"He's unbelievable out there," Harden said of Crisp. "I've been watching him make plays like that all season. To be pitching when he does it, it was great."
Harden retired 16 of his first 18 hitters before Johnson doubled and scored on Drew's hit.
"He threw a lot of strikes," Johnson said. "He's got a reputation for a lot of high-pitch counts early, and I think in the beginning we wanted to see how he was going to come in and pitch."
Harden has had trouble staying healthy for most of his career. He just finished his 10th visit to the disabled list, and hasn't pitch a full season since 2004.
The A's also recalled RHP Fautino De Los Santos from Triple-A Sacramento, optioned RHP Trystan Magnuson to Sacramento and designated LHP Bobby Cramer for assignment. ... Arizona promoted INF Sean Burroughs from Triple-A Reno, reinstated RHP Sam Demel from the DL and placed RHP J.J. Putz on the DL. ... A's manager Bob Melvin announced a one-time six-man rotation to protect Harden. Josh Outman, Gio Gonzalez, Brandon McCarthy (currently on the DL with a stress reaction), Trevor Cahill and Guillermo Moscoso will follow the righty. ... Drew has reached safely in 16 of his last 17 road games.