DETROIT -- Both Nate Robertson and Jeremy Bonderman were back at Comerica Park on Wednesday, encouraged by their outings the previous night at Triple-A Toledo to start their Minor League rehab assignments. But both see a lengthy stint ahead before they're ready for a return to the big leagues.

Robertson started Tuesday's game for the Mud Hens and gave up a run on four hits over his 2 2/3 innings, throwing 39 pitches. Three of those four hits, including an Andy Green home run he allowed for his lone run, came in his third and final inning of work as his arm started tiring.

He wasn't throwing completely free and easy, but he believes the tightness came more out of lack of work than from any effects of the surgery he had at the end of June to remove tissue masses from around his elbow.

"Just that breakdown before I build things up, that's the process, that's the stage I'm in right now," Robertson said. "I think that once I get over this hump, there should be a difference that I feel. I think I'll start feeling that difference once that fluid and that swelling goes away."

The bright side, Robertson said, was that his command of his pitches was solid. Usually that's one of the last aspects to return after surgery.

Bonderman's perfect inning not only included good arm strength, but it also had a pitch or two he had never thrown in a game. He threw a splitter, he said, as an offspeed pitch, throwing it once for a called strike and again for a swing and miss.

"It felt good just to play," Bonderman said. "It's been a long time."

Robertson will start again for the Hens on Saturday, when he's expected to throw about 50 pitches. He'll be on a regular schedule to pitch every five days after that, extending about 10 pitches per outing until he stretches his arm to about 100 pitches.

Bonderman will continue to work out of the bullpen, with his next appearance on schedule later this week, then on an as-needed basis soon after.