Joe Mauer had seen the slider thousands of times, the way it buzzed toward the plate looking like a down-the-middle mistake, then suddenly swooped down and away, frequently winding up in the righthanded batter’s box. Mauer caught it so often, he could practically do it with his eyes closed, shifting his weight to the left and turning his glove to backhand the ball.

Then he stood in the batter’s box himself, and Francisco Liriano threw the same pitch Mauer knew so well. Suddenly, everything changed.

“I can see why he’s had so many swing-and-misses over the years,” Mauer said.

He’ll get another close-up look Tuesday, when the Twins come face-to-face with a player whose slider electrified Minnesota during a memorable rookie year in 2006, but became frustratingly inconsistent after elbow surgery sidelined him for 18 months. Liriano, now a reliable, established veteran in Pittsburgh’s rotation, will start for the Pirates in Tuesday’s interleague series opener, the first time he’s faced the Twins since joining the Pirates in 2013.

“It’s going to be fun,” said Torii Hunter, another former teammate. “Frankie, he’s like one of my boys.”

Mauer caught Liriano 85 times over their seven seasons as teammates, more than twice as much as any catcher during the lefthander’s career, but he’s only batted against him twice. Three days after the Twins traded Liriano to the White Sox in 2012 — the Twins received Eduardo Escobar and since-released lefthander Pedro Hernandez in return — he pitched against his old team, and Mauer batted three times. He swung at and missed a slider for a three-pitch strikeout. He stood frozen and watched another strike three. Having learned his lesson, Mauer also waited out a four-pitch walk.

“I realized, as much as you see it catching, when you’re standing up there as a lefthanded hitter, that slider is really different,” Mauer said. “On stuff alone, he’s one of the best pitchers I’ve ever caught. We know what we’re getting into when Frankie is on the mound.”

So does Hunter, who has faced Liriano 21 times in seven games. He is 5-for-18 with a home run and three walks, but four strikeouts.

“I think he’s gotten smarter about pitching. When he was young, he was a thrower, with that great pitch. Now he knows how to use it better,” Hunter said. “You can tell he studies hitters. He mixes it up. He knows more about pitching.”

The two-game series might have been a double reunion, because Vance Worley, the Twins’ opening day starter in 2013, has followed Liriano in the Pirates’ rotation. But Worley hasn’t pitched well lately, giving up 17 hits and eight runs with no strikeouts in his past two starts, so with an off day Monday, the Pirates chose to skip his turn this week in favor of lefthander Jeff Locke.

But the Twins still are interested in seeing Liriano, who despite a 1-3 record has pitched very well this season, posting a 2.96 ERA and striking out 50 in 45⅔ innings.

“Liriano’s got that wipeout slider, and it looks awfully impressive on the TV games I’ve seen,” General Manager Terry Ryan said. “That’ll be a huge challenge for us.”

Liriano was once a reclamation project for the Pirates, his career in doubt after he pitched inconsistently following the trade to Chicago. But he owns a 24-21 record in Pittsburgh with a 3.17 ERA, and signed a three-year, $39 million contract with Pittsburgh last winter. With a $13 million average salary, he’s earning roughly the same as the Twins pitcher he will face, Ricky Nolasco.

“I’m really happy for Frankie,” Mauer said. “He’s a great guy, and someone you know will really compete.”

“We just give each other the head nod when I come up to bat. ‘Nice to see you, Frankie.’ ‘What’s up, T?’ “ Hunter said. “Then he tries to strike my butt out.”