PHOENIX -- It was a duel for the aged.
"It was just a matter of who gave up the least amount of runs," said Wells (1-1), who gave up five in five innings.
Six months after back surgery, Johnson (0-1) gave up six runs and six hits in five innings against San Diego, his first start for the Diamondbacks since 2004. The Big Unit allowed two home runs and two doubles. He walked four -- two intentionally -- hit two batters and threw just 53 of 97 pitches for strikes.
"I thought everything went pretty well," said Johnson, who struck out seven. "It's not the way I would have written things up."
Arizona (10-11) lost its fifth straight and dropped below .500 for the first time since April 4.
Johnson said there was "absolutely no comparison" to how he felt at the end of last season.
"I don't want to hash out last year," Johnson said. "I'm looking forward to this year.
"The bottom line is, I'm looking for results," Johnson said. "Spring training's over for me."
Born May 20, 1963, Wells is nearly four months senior to Johnson, born Sept. 10 that year. At a combined 87 years and 300 days, they broke the previous mark for oldest duo of lefty starting pitchers, set April 12 when 44-year-old Jamie Moyer of Philadelphia opposed 41-year-old Tom Glavine of the New York Mets.
Wells said he didn't feel bad about beating his "younger" rival.
"He's gotten the better of me quite a bit," Wells said. "It's nice to put him through the ringer instead of me."
Khalil Greene matched his career high with four hits and had four RBI, three on a bases-clearing double, as the Padres won for the fourth time in five games. Adrian Gonzalez went 3-for-3 with a homer and a double and three RBI.
Greene said he was impressed with Johnson.
"Just the stuff he was throwing, he was pretty sharp," Greene said. "He was throwing hard, and his slider had good depth on it."
Johnson pitched a perfect game for Arizona three years ago, then spent two frustrating seasons with the New York Yankees, failing to win both of his postseason starts. Johnson, who needs 20 victories for 300, pitched in Phoenix for the first time since Oct. 2, 2004, when he defeated the Padres.
He began his season late following back surgery last fall.
Arizona managed three runs in losing all three games of a weekend series at San Francisco but had little trouble hitting Wells. The Diamondbacks took a 2-0 lead on a homer by Carlos Quentin, who entered with a .167 average.
San Diego tied it at 2-2 in the third on Gonzalez's 396-foot, opposite-field shot into the left-field seats.
Drew, hitting .209, put the Diamondbacks ahead 3-2 with an RBI single in the third.
That wasn't enough support for Johnson, who no longer has the overpowering fastball and biting slider that helped him win five Cy Young Awards, four with the Diamondbacks.
"I thought he threw the ball pretty well, especially early on," Melvin said.
After one time through the batting order the Padres began to tee off.
Johnson gave up a tying solo homer to Jose Cruz Jr. in the fifth, and Greene hit a three-run double to put San Diego up 6-3. Wells gave up two more runs in the bottom of the inning, but the Padres answered with four in the sixth to take a 10-5 lead, and Wells turned the game over to San Diego's sturdy bullpen.
"It's nice to see that big number up there, but it seemed like if I had stayed in there, I would have given it right back to them," Wells said. "Everything I threw looked like a meatball. I got lucky."
Even with a five-run lead, Black didn't hesitate to call upon baseball's all-time saves leader. Hoffman hadn't pitched in five days.
"Anytime a team is one swing of the bat from getting real close, we don't want to take a chance," Black said.
- Johnson's homecoming did not create a rush to the box office. On a night the Phoenix Suns had a playoff game two blocks away, the Diamondbacks drew 19,508, Arizona's smallest crowd in nine home dates.
- The Diamondbacks are 4-0 against Washington and 6-11 against everyone else, including 4-10 against the NL West.