"I've got to figure something out in the first inning," Wood said. "The last two times I've pitched, the first inning has been kind of rough."
Brian Giles and Ryan Klesko also homered off Wood (0-1), who gave up four runs in the first inning. Wood wound up allowing seven runs, one of them unearned. He needed 51 pitches to get through the first two innings and threw 112 by the time he left after Klesko's drive with two outs in the seventh.
Wood gave up one run on a double and a walk in the first inning of a no-decision on April 8 against Milwaukee.
"Early on he didn't have a feel for his breaking ball," Cubs manager Dusty Baker said. "There's no need for concern. He settled down after that first inning and found his release point...I'm sure he'll be better the next time out."
Jake Peavy (1-0) gave up two runs and six hits in seven innings, striking out seven and walking one.
"He came through with seven solid innings," Padres manager Bruce Bochy said. "That's what you want in the first game of a doubleheader."
Blum also homered leading off the ninth against left-hander Cliff Bartosh, the third time he homered from both sides of the plate in one game. Xavier Nady went 4-for-4 with a pair of doubles for the Padres, tying a career high for hits.
In the second game, Mark Prior made his first start of the season for the Cubs, with Brian Lawrence pitching for San Diego.
Peavy, who blanked Pittsburgh for 6 2/3 innings in his first start, gave up his first runs of the season in the fourth when Corey Patterson homered and Jeromy Burnitz hit a sacrifice fly. With the bases loaded and two outs, Peavy struck out Todd Hollandsworth.
"That could've been the turning point of the game and luckily we got out of it," Peavy said.
After Blum's first homer, Wood loaded the bases by hitting Mark Loretta in the hip with a pitch, then walking Brian Giles and Klesko on a total of nine pitches. Phil Nevin hit an RBI grounder, Ramon Hernandez had an RBI single and Nady hit a dribbler to Wood, who threw wildly to first as another run scored.
"When you give up four in the first against a guy like Peavy, you're not giving your team much of a chance," Wood said.
Giles homered in the second for a 5-0 lead and had a sacrifice fly in the seventh before Klesko's homer. The wind was blowing in at 16 mph at the game's start.
"I was surprised to see the balls leaving the park today, no question," Wood said "It makes me wonder how far they would've gone if the wind was blowing out or not blowing in."
Adam Hyzdu made a running catch in the seventh on a Michael Barrett fly ball to left, fell down and threw to second to double up Derrek Lee.
- Blum homered from both sides on July 5, 2001, for Montreal against Florida and last May 4, 2004, with Tampa Bay at Texas. It was his fourth career multihomer game and also his first time leading off a game with a homer.
- Baker would have preferred to make up Tuesday's rainout on Thursday, an off day for both teams. If the Padres played Thursday, they would be scheduled for 22 straight days, which would need players' permission. "One peril of playing an unbalanced schedule right here is a team only comes here once," Baker said. "You have to play a doubleheader or play on the off day or come back late in the year."
- Barrett threw out his third runner of the series, getting Klesko at second base in the fifth inning.
- Mike Fontenot made his major-league debut for the Cubs, pinch running and scoring in the ninth inning.