"I'm a little disappointed," said DeFrancesco, who's 1-7 since taking over for Brad Mills on Aug. 19. "We had the chance to win the game there in the ninth inning. You've got to remember we're going against a pretty good team."
The Astros, who watched the Mets hit a walk-off homer to win in the ninth inning Sunday in New York, fell to 38-6 when leading after eight innings. The Giants improved to 15-5 on the road since the All-Star break.
"This was great for us," Cain said. "That's what you want to be able to do, especially with only three outs left. I think it's going to build a lot of momentum for us for the week."
Cain, who threw a perfect game against the Astros on June 13, turned in another gem, but was in line to get the loss after Jimmy Paredes -- in his first game since being called up from Triple-A Oklahoma City -- led off the eighth with a walk and wound up scoring on a wild pitch to give the Astros a 2-1 lead.
Brandon Belt led off the ninth with a single against Wesley Wright and scored from first on Arias' pinch-hit double down the left-field line against Wilton Lopez. After Brandon Crawford struck out, Sanchez pinch-hit and singled to center to score Arias.
"The three games in New York were very close and this game's close -- another one-run game," DeFrancesco said. "Eventually it's going to turn. We've got a lot of confidence in those guys there. The effort's there. I'm watching them go hard every day. It's kind of frustrating for the manager and coaching staff not to get a 'W' after a game like that."
Fernando Martinez homered and Brett Wallace was 3-for-4 to tie a career high for hits. But Houston was 0-for-10 with runners in scoring position, failing to take advantage in the fourth, fifth and sixth when it had runners in scoring position and less than two outs.
"Young hitters in that situation, it's going to take experience for these guys to drive in runs," DeFrancesco said.
Astros starter Bud Norris was every bit as good as Cain before another injury forced him to the showers early. He left a game with an injury for the fourth time this season, walking off the mound with two outs in the seventh after suffering a blister on his right middle finger.
"I've had it on and off in my career," Norris said. "It's going to be OK. I've just got to manage it. It's something I've dealt with. It kind of came in the second and third inning, and it really starting hampering me later in the game, and I think they made the right move by doing that right there."
Norris held the Giants to six hits and one run and struck out seven in 6 2/3 innings, but remains winless since May 21, a span of 15 starts. He left his Aug. 15 start at the Cubs with a bruised foot, his June 12 start at the Giants with a sprained left knee and his May 13 start at the Rockies with a strained hip flexor.
"You never want to be, not necessarily injured, but having little things flare up is not always fun," Norris said. "You always pray for a healthy season and that's my goal and it's going to happen. Starting pitchers go through peaks and stuff, but I've got to keep battling and that's what I'm going to keep doing."
Norris has 14 quality outings in 24 starts, but the club has scored three or fewer runs in 11 of his last 15 outings. As far as the blister, he called it an "occupational hazard."
"I just have to manage it day by day and go from there," he said.
Angel Pagan led off the fifth with a homer to right field to give the Giants a 1-0 lead, but the Astros answered in the bottom of the inning when Martinez hit an upper-deck shot to right to tie the game.
"That's the guy we're looking for -- power guy who can drive a baseball," DeFrancesco said. "He's making some adjustments up here, too."
Cain hadn't allowed a hit through three innings, retiring nine of the first 10 batters he faced. Wallace collected the Astros' first hit with a double to left-center field in the fourth, but he was stranded in what became a familiar theme.