"I stayed back and waited for a slider or changeup," Infante said. "He threw a fastball and I made a good reaction."
Left-hander Drew Smyly, who was beaten out by Porcello in a spring training competition for the final spot in the Detroit rotation, came on in relief in the seventh and struck out the only two hitters he faced.
Joaquin Benoit allowed Upton's homer in the eighth, but Detroit came back with a couple insurance runs. Infante's one-out double made it 6-4, and after he stole third, Austin Jackson walked. Cabrera's two-out single to center gave the Tigers a three-run lead.
The Tigers were prepared to let Valverde leave as a free agent after he struggled at the end of last season, but they brought him back on a minor league deal and eventually called him up this week.
He worked a 1-2-3 ninth for a save against Kansas City, and Saturday's appearance was even more impressive. He struck out B.J. Upton and Juan Francisco to end it.
The Braves are 3-7 since their 12-1 start.
Medlen and fellow starter Paul Maholm were breezing through the early part of the season for the Braves before coming to Detroit. Then Maholm was knocked around in a 10-0 loss to the Tigers on Friday, and Medlen allowed 10 hits in 5 1-3 innings the following afternoon.
"Hanging curveball to Peralta — can't give him one there — and that pitch to Omar that was out over the plate," Medlen said.
Porcello, on the other hand, left to a standing ovation in the seventh. He couldn't match Anibal Sanchez — who set a franchise record for Detroit the previous night with 17 strikeouts — but this was a step in the right direction.
NOTES: Cabrera extended his hitting streak to 11 games. ... Atlanta had been 15-0 when hitting at least one homer, but that streak came to an end Saturday. ... Detroit's Doug Fister (3-0) takes the mound Sunday night in the series finale against Atlanta's Mike Minor (3-1).