PITTSBURGH (AP) _ Kordell Stewart threw a touchdown pass before being lifted for precautionary reasons with a sprained knee and the Pittsburgh Steelers remained unbeaten in the preseason, beating the Detroit Lions 28-20 Sunday night.

The Steelers (4-0), enjoying their first winning preseason in Bill Cowher's six seasons as coach, blocked a punt for another touchdown to withstand Glyn Milburn's 84-yard TD return of the second-half kickoff.

Milburn's touchdown gave the Lions a 17-14 lead, but Mike Tomczak _ last season's starter and now Stewart's backup _ answered by hitting Henry Bailey on a go-ahead, 32-yard scoring pass play 4:56 into the second half.

All three Steelers quarterbacks who played threw for touchdowns. Mike Quinn, an undrafted rookie from Stephen F. Austin, sealed the victory by connecting with rookie Michael Adams on a 78-yard scoring pass play with 2:17 remaining.

With a steady and occasionally driving rain falling throughout, the Lions held out quarterback Scott Mitchell because of a strained groin. Coach Bobby Ross apparently did not want to risk him possibly aggravating the injury by slipping on the wet turf.

Frank Reich, formerly Jim Kelly's backup in Buffalo, started for Mitchell and was 11-of-17 for 95 yards and an 11-yard TD pass to Herman Moore. Moore's scoring catch came after Luther Elliss recovered Jerome Bettis' fumble on the Steelers' initial possession.

Stewart was injured as Lions nose tackle Shane Dronett hit him below the knees just after he released a pass on a third-and-10 play from the Steelers' 14 midway through the second quarter. Dronett drew a 15-yard roughing the passer penalty.

Stewart immediately got to his feet, but did not return after team doctors diagnosed a sprained left knee ligament. He spent the rest of the half flexing the leg, doing knee bends along the sidelines and explaining to his teammates how he was hurt.

Stewart, the Steelers' third starting quarterback in as many seasons, was 7-of-11 for 84 yards and a touchdown. He is 26-of-41 for 347 yards, four touchdowns and no interceptions in four preseason games, but will likely sit out Friday's exhibition finale at Carolina. He is expected to undergo additional tests Monday.

Steelers fullback Tim Lester also left after fracturing his left hand during the first quarter, but it was not known how long he would be out.

Before being lifted, Stewart followed Reich's scoring pass by finding former Colorado teammate Charles Johnson on a 26-yard touchdown pass play. Stewart was 4-for-4 for 67 yards on the drive after the Steelers lost nine yards on their first seven plays from scrimmage.

After the Lions gained only two yards on their subsequent possession, Chris Oldham broke up the middle to block backup punter Andy Caflisch's punt and Myron Bell returned it 18 yards to score, putting the Steelers up 14-7. The block came on only Caflisch's second punt of the preseason.

Jason Hanson kicked field goals of 26 and 43 yards for Detroit. Steelers kicker Chris Jacke was held out with a groin injury, and rookie replacement Sean Reali did not attempt any field goals.