SAN FRANCISCO — The Giants were one pitch away from a victory that would’ve satisfied two sets of orange-clad fans Monday night.Rookie right-hander Blade Tidwell flashed dominant stuff into the sixth inning while holding the Houston Astros to one run. Center fielder Drew Gilbert hit a tiebreaking home run in the seventh and leapt at the warning track to take away an extra-base hit in the ninth. Giants manager Tony Vitello coached both players at the University of Tennessee. Everything pointed toward a rare night for Vitello to celebrate in what’s been a difficult maiden season in pro baseball.But there was no Knoxville-themed party. Just another night in a season of hard knocks.The Giants could not protect a one-run lead in the ninth in an eventual 6-3 loss. Right-hander Dylan Smith issued a one-out walk and threw a wild pitch that moved pinch runner Nick Allen to second base, then Allen raced home after Cam Smith’s slow ground ball ticked off the glove of second baseman Osleivis Basabe and trickled into right field. The Astros scored their placed runner in the 10th inning, plus some more, against right-hander Jason Foley — another walk! another wild pitch! — and in the bottom of the 10th, Vitello passively sent up three left-handed lambs against Astros left-handed closer Josh Hader to bring a feeble end to the night on the shores of McCovey Cove.The Giants dropped to 49-70, and are 21 games under .500 for the first time since the last day of their 98-loss season in 2017. They’d have to go 14-29 or better the rest of the way to avoid the second 100-loss season in the franchise’s West Coast era, and with a roster that’s been depleted by injuries and the trade deadline, there appear to be no depths to which they cannot sink.It turns out that failure, no matter how spectacular it might be, does not make for compelling viewing. The announced attendance of 28,070 marked the first time all season that the Giants failed to draw 30,000 fans.After the game, Vitello was asked why he took out Tidwell with two out and two on in the sixth, passing up what might have been a learning moment for the rookie right-hander. Vitello’s answer revealed more than the thought process behind one pitching change.“There’s a whole basket full of learning points that everybody behind me, and me, need to learn from and move forward,” Vitello said. “And at the same time, we’re kind of out of room for learning points. I realize we’re at a point in the year where we’re trying to give some guys some looks, if that’s a fair way to say it. But we’re trying to win ball games.”When it comes to winning close and late, they’ve got plenty left to learn. The Giants are 10-20 in one-run games. Dylan Smith has been walked off in four different ballparks, and although it’s impossible to get walked off at home, his luck this season has been so lousy that he might find a way to do it. The Giants aren’t getting any breaks, nor are they finding ways to create them. They took another gut punch prior to Monday’s game when they learned that rookie catcher Daniel Susac had sustained a season-ending fracture to his left kneecap on Sunday, prompting them to call up yet another organizational player from a minor-league system that’s already been scrubbed of them.