Hamels has been nursing a right oblique strain since early last month. He was placed on the disabled list on May 2 for the first time since joining Texas at the trade deadline in 2015.
The four-time All-Star threw 35 pitches during Friday's outing, plus an additional 22 in a bullpen session.
"It's more spring training velocity right now," Hamels told the Dallas Morning News afterward. "Once you get to 90-100 pitches, that's where you develop the endurance and strength. It is what it is right now."
Hamels is 2-0 with a 3.03 ERA in five starts this season.