OAKLAND -- There's no such thing as having too much pitching. The Astros are all too aware of that just one week out from the Trade Deadline.

While Houston has boasted one of the most successful rotations in the American League this season, it was starting pitching that sunk the team Monday night in a 7-5 series-opening loss at the Oakland Coliseum, snapping a five-game winning streak coming out of the All-Star break.

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Jake Odorizzi's start was his third straight appearance against the A's. He had been dominant in his first two, allowing three runs on nine hits across 12 1/3 innings, striking out 12 against one walk.

But Odorizzi could not replicate his previous results. He allowed a season-high six earned runs over five-plus innings while dealing with a blister that formed on his pitching hand.

"I don't know," manager Dusty Baker said. "[The familiarity] might have had a factor in it, but a couple pitches … when you miss location, sometimes that's what happens."

Odorizzi cruised through the first two innings, retiring six straight A's batters. That's when the blister began to form on his right middle finger.

"The callus on my finger started fraying off, and every pitch I was throwing, just kept getting a little more ripped," said Odorizzi, who described the pain as a "shocking, stinging sensation."

From there, Odorizzi began to unravel slowly, starting when he gave up a solo home run to former Astro Tony Kemp in the third inning. He settled down and retired the next three batters, but the dagger came in the fourth inning, when Oakland put up a five-spot.

Though he acknowledged that the pain affected his performance, Odorizzi maintained that his execution was off during that inning, particularly on his cutter and slider.

"Having seen these guys a lot the past three times, they kind of know my shapes at this point," Odorizzi said. "If my execution isn't right on point, then obviously it's a more hittable pitch if they've seen it quite a bit, which a lot of them have because that's our game plan against them."

Following the five-run fourth, Odorizzi popped the blister and breezed through a six-pitch fifth inning. But the damage was done. Odorizzi said he expects to be fully healthy for his next turn in the rotation, but if the blister continues to bother him, the Astros should have no problem skipping his start, as the team has employed a six-man rotation ever since Odorizzi returned from a six-week stint on the injured list in early July.

Astros starters lead the Majors with 49 wins, and their 3.18 ERA is the best in the American League -- but that might not stop the team from adding more starting pitching depth before the Trade Deadline on Aug. 2.

One primary target for Houston may be the Reds' All-Star starter Luis Castillo. MLB Network insider Jon Heyman reported in the New York Post that the club is "showing keen interest" in the right-hander.

Castillo has gone 3-4 with a 2.77 ERA for the scuffling Reds this season, and his addition could be the boost any contender would need to make a deep playoff run. But the price tag will likely be steep, as the 29-year-old has an extra year of club control beyond this season.

The Astros can choose to stick with their internal options, but general manager James Click has signaled that the team will be active at the Deadline.

"We have been doing everything we can to get the trade market moving, but a lot of teams focused on the Draft for the last week or so," Click told AT&T SportsNet Southwest on July 21. "Now that we're through it, we are continuing to work the phones. 

"We are putting all the balls in the air. We are being as aggressive as we possibly can, because we think that this team has a chance to do something really special, and our job is to give them what they need in order to complete that."