Sanchez iced the Cubs with a pinch-hit single in the 16th inning that gave the Bucs another walk-off win, 4-3, before the remaining PNC Park crowd of 29,762.
The rookie emerged from the dugout in what already was the longest baseball game, in terms of time (five hours, 55 minutes), ever in Pittsburgh for his first at-bat of the season.
Jordy Mercer had begun the 16th with a single off Carlos Villanueva -- also the loser in Monday's Opening Day affair, on Neil Walker's 10th-inning home run. Jose Tabata bunted into a force, then sped to third on Starling Marte's single.
Manager Clint Hurdle called on Sanchez to hit for Stolmy Pimentel who, validating the decision to pack two long men in the bullpen, had blanked Chicago for four innings on two hits.
"I tried to stay awake as long as possible," Sanchez said with a grin. "It's not easy, sitting down for 16 innings. But Marte set the table, made it real easy for me."
Sanchez took a couple of balls -- then his first swing of the season sent the ball onto the left-center grass, sent Tabata across the plate and sent everyone else out of the Pirates' dugout.
"A thing of beauty for us," said Hurdle. "This, obviously, was a game better to win."
The manager alluded to the mutual toll. He used seven pitchers, Chicago counterpart Rick Renteria called on nine.
"We'll figure out the pitching [going forward] tomorrow," said Hurdle, who meant "today" since Thursday's afternoon game was to begin less than 12 hours after this one wrapped.
At five hours, 55 minutes, it was the longest home game in Pittsburgh's 128-year history, surpassing the five hours, 49 minutes it took the Bucs to beat Houston in 18 innings on May 27, 2006.
Hurdle had watched, and marveled, as his entire bullpen -- with the exception of Monday's winner Bryan Morris -- repeatedly turned away the Cubs after a sore left thumb had forced out starter Charlie Morton after six innings.
"You gotta love the work we were able to do off the mound," Hurdle said. "The way we stranded people on the bases was just fantastic. Both teams had opportunities to put this game away before it got taken care of."
Indeed. The Bucs and the Cubs aren't exactly putting on a clutch-hitting clinic. Between them, in the two extended games they have produced four hits with men in scoring position -- in 42 at-bats.
Nate Schierholtz's sixth-inning liner had caromed off Morton's mitt, and it became an inning-ending double play. By the time he reached the dugout, Morton couldn't close his gloved left hand.
"He had to come out," Hurdle said of Morton, on whom subsequent X-rays were negative.
The teams had exchanged 12th-inning runs, Anthony Rizzo's homer off Jeanmar Gomez in the top getting neutralized by Marte's two-out RBI single off Jose Veras in the bottom.
This is the first season the Pirates have opened with consecutive extra-inning games since 1964 -- when they had split them with the Cubs, that time in Forbes Field.
Until his abrupt departure, Morton had been a mirror image of Francisco Liriano on Opening Day. The right-hander mimicked the lefty's six shutout innings of four-hit ball.
And, like Liriano, Morton had to settle for a no-decision when Emilio Bonifacio, who entered the game hitting .800 and finished hitting .750, lined his fourth hit to set up the Cubs' tying rally in the ninth off closer Jason Grilli.
Grilli had entered to protect a 2-1 lead, and he surrendered a one-out single to Junior Lake. Bonifacio's two-out single kept the inning alive for Luis Valbuena, who ripped another single to right to make it 2-2.
Pittsburgh's shutout season had ended at 17 innings, with the help of the new extended replay review system.
With the bases loaded and one out in the eighth, and the Bucs holding a 2-0 lead, Schierholtz appeared to ground into an inning-ending double play.
But Renteria came out to challenge that second baseman Walker's throw had pulled shortstop Mercer off the second-base bag before his relay throw to first.
Following a 2-minute, 24-second review, second-base umpire John Tumpane's out call at second was overturned -- on the basis of that wide throw since, in spirit, the so-called "neighborhood" play at the keystone is not open to challenge. And since Rizzo was safe at second, the run Bonifacio scored from third was added to the board.
The inning continued, but it soon ended as Mark Melancon got Ryan Sweeney to ground out to second, with the Bucs still leading, 2-1.
The Bucs' first hit of the season with a runner in scoring position came from an obvious source. Mercer, whose 2013 average of .308 in those situations was about 80 points above the team norm, singled with one out in the second to score Walker from second for a 1-0 lead.
Pittsburgh doubled that to 2-0 in the sixth, when Cubs shortstop Starlin Castro let Russell Martin's grounder through him for a two-out error that escorted Marte home from second base.
The Clark Kent Syndrome was again very evident with Morton. Otherwise very soft-spoken and mellow, Morton's phone booth is the pitcher's mound. Get him on it, and he becomes a fierce competitor for truth, justice and the Pirates' way.
Edwin Jackson plunked leadoff hitter Marte in the bottom of the first. Morton's next pitch, to Rizzo starting off the second, bounced off the Chicago first baseman's leg.
Plate umpire Bob Davidson promptly gave both benches the early warning. But Morton had already issued his own warning.
And it was not exactly out-of-character. In 2013, Morton led National League pitchers with 16 hit batsmen, remarkable if only because he did not begin pitching until June 13 and sent all those messages in only 116 innings.