"It was a real good pitch to hit," Hafner said, and hit it he did.
A streak of 163 consecutive Angels triumphs when carrying a lead into the ninth inning finally ended with manager Mike Scioscia looking to Darren Oliver and Speier to handle roles generally entrusted to Scot Shields and Francisco Rodriguez.
Oliver got five outs in the seventh and eighth, with Speier coming on to strike out Casey Blake to strand two runners in the eighth.
On the verge of nailing down his first save of the season, Speier watched it get away by the razor's edge of the full-count pitch to Asdrubal Cabrera, followed by the fateful slider that slid into Hafner's power zone.
"Anybody holding a bat is dangerous," Speier said, trying to handle K-Rod's role as he nurses a tender right ankle. "I just made a mistake -- middle up. No excuses. I made some good pitches with the slider to lefties. I just made a bad pitch there."
Jake Westbrook, a study in efficiency and economy, needed only 94 pitches to pick up a complete-game victory and move to 1-1 by keeping the Angels silent for eight of his nine innings.
But one bad round had Westbrook on the ropes, one strike to Cabrera away from defeat, when Hafner unloaded his second homer of the season.
A two-run bomb by Vladimir Guerrero -- on another slider that stayed in a hitting zone -- had followed singles by Erick Aybar and Chone Figgins and a sacrifice fly by Gary Matthews Jr. in the sixth inning, turning a one-run lead over to Oliver and Speier.
"It was a slider that just kind of spun," Westbrook said of Guerrero's first homer of the season. "He doesn't miss too many mistakes ... and he definitely didn't miss that one."
The full-count walk to Cabrera preceding Hafner's second homer of the season was pivotal.
"I had Cabrera 1-2 [in the count], threw a couple forkballs off the plate a little bit and just didn't make a good [3-2] pitch," Speier said. "I had that ball being up for him, a ball. Definitely."
Santana's second start was solid: six innings, six hits and three walks, two earned runs and five strikeouts.
"I thought Ervin had good stuff," Scioscia said. "He pitched out of trouble, and had really good life on his fastball early. He made some key pitches to give us a chance to win. We just couldn't finish it off."
The manager maintained his position that the bullpen is in capable hands at the back end, even with Shields recapturing his form after a fitful spring (shoulder, forearm issues) and K-Rod testing a new delivery to ease stress on his ankles.
"There's nobody that doesn't have confidence in what Darren and Justin bring into a game," Scioscia said. "They did it last year. You're not going to have a full contingency of arms on a given night. There were times when Shieldsy and Frankie were down and we won games."
After letting an opportunity get away in the first when Hafner was thrown out at home on Victor Martinez's double to right, the Indians took advantage of a leadoff walk by David Dellucci and Blake's single to grab a 2-0 lead in the fifth on Cabrera's two-out single to right.
Santana wrapped up his work when he escaped a bases-loaded predicament in the sixth and turned it over to Oliver after Guerrero's mammoth blast.
Oliver got a double play on Hafner to close out the seventh and then two more outs in the eighth, leaving two on for Speier, assuming K-Rod's role. Speier put Blake away on a check swing and was a strike away in the ninth when disaster struck.
"Frankie's the best in the business," Speier said. "When we're running on all cylinders, it's nice to have him there. We're going to pick up the slack."