Infante's homer came on an 0-2 pitch — after Alex Avila drew a two-out walk to keep the fourth inning going.
"I stayed back and waited for a slider or changeup," Infante said. "He threw a fastball and I made a good reaction."
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.
Medlen (1-3) 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.
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).