With the bases loaded, two outs in the ninth and the Padres trailing Milwaukee by three runs, Blum drove a fly ball to right field and started what he thought would be a home run trot.
But the ball held up and Geoff Jenkins caught it on the warning track, and the Padres were brought back to reality in a 5-2 loss.
The defeat came one day after the Padres completed their best month ever by going 22-6 in May. It also ended their club-record 11-game home winning streak and their six-game overall winning streak.
"I thought I just hit it good enough," said Blum, who hit a tiebreaking three-run homer in an 8-4 win on Tuesday night. "No matter what the situation is, four runs in the ninth inning is no big deal to us."
After Doug Davis held the Padres to one run through eight innings, Derrick Turnbow started the ninth but left after allowing Miguel Ojeda's RBI single and walking pinch-hitters Mark Sweeney and Ryan Klesko to load the bases.
Julio Santana relieved Turnbow and retired Khalil Greene on a popup to second and then Blum to earn his first career save.
"He had a lot of the clutch hits in the series and he definitely was the one guy we just did not want to see up there right then," Jenkins said. "He hit it hard. This is not the park you're going to see a ton of homers in."
Said Brewers manager Ned Yost: "Nothing comes easy, that's for sure."
Carlos Lee and Jenkins homered off ineffective Brian Lawrence for the Brewers, who snapped a four-game losing streak. Jenkins had three RBI and Damian Miller had three of Milwaukee's 15 hits. Brady Clark, who graduated from the University of San Diego in 1996, singled in his first three at-bats and scored twice for the Brewers.
Davis (7-5) won his third consecutive start. He held the Padres to one run and six hits, struck out seven and walked three. He's given up just one earned run in his last three starts.
Davis extended his scoreless streak to 20 2/3 innings before Xavier Nady hit an RBI single with two outs in the fourth to make it 5-1. Nady's hit scored Blum, who hit a leadoff single and took third on Phil Nevin's single, which bounced off second base and into center field.
Lawrence (3-6) threw 117 pitches in 5 2/3 innings and was booed several times. He allowed five runs and 12 hits, which tied his career high. He walked four and struck out three. He was coming off his seventh career complete game, a 9-3 win at San Francisco on Friday.
Lawrence was hit hard from his first pitch, which Brady lined into center field. Bill Hall singled, Jenkins hit a sacrifice fly and Lee homered off the facade of the second deck in left field to make it 3-0. It was Lee's 13th.
"He had trouble hitting the spots," manager Bruce Bochy said. "He was a little off. He was catching too much of the plate. But he battled there. We needed him to pitch some innings tonight."
On Tuesday night, ace Jake Peavy went just four innings.
The Brewers loaded the bases later in the first with two outs before Lawrence struck out Davis.
Clark singled leading off the second and scored on Jenkins' one-out double to left. Jenkins made it 5-0 in the fourth with his leadoff homer to right, his fifth.
- Brewers 3B Russell Branyan fractured his left middle finger attempting to bunt in the seventh inning. If the swelling subsides, he thinks he can keep playing. Otherwise, he said he might be out two weeks.
- J.J. Hardy was the only Brewers regular not to get a hit off Lawrence, but he did draw two of his three walks off the right-hander.
- Padres RHP Woody Williams, on the disabled list since May 2, is scheduled to throw long toss on Thursday. Williams threw 60 pitches in a simulated game on Tuesday. Bochy said Williams is likely to pitch somewhere on Saturday or Sunday, most likely on a minor-league rehab assignment.