Langer, the Champions Tour money leader, finished with an even-par 70 to put him at 2-over 212 for the tournament, a shot ahead of Haas and local favorite Jeff Sluman.
Haas vaulted into contention with an eagle-2 from the rough on the second-to-last hole, but then closed with a bogey to cap a 72. Sluman was among the leaders, but was undone by closing with three straight bogeys for a 70.
Scott Simpson and Bill Britton were tied at 216 and Greg Norman was part of a four-man group at 217. Otherwise, theres no one else close entering the final round of the $2 million tournament at an ever-stingy East Course thats surrendered only nine sub-par rounds over the first three days.
The field opened up significantly with only eight players within six shots of the lead. That comes after the day began with 25 players within six shots of the lead once held by Tom Purtzer, who tumbled down the leaderboard after shooting an 82 that put him in a tie for 25th.
Langer and Sluman spent most of the day tied for the lead and appeared in a position to run away from the field after the playing partners both scored birdies on the 14th and 15th holes. That put them five shots up on the nearest contender.
Then came an uncharacteristic collapse when both carded bogeys on 16 and 17.
Sluman added another bogey on 18, and Langer nearly did so too if not for a clutch 6-foot putt to save par.
Haas, in the meantime, went on a roll after struggling through a round that appeared to be going nowhere, and had him sitting 4-over for the day through 14 holes.
After a birdie-2 on No. 15, Haas produced one of the best clutch shots of the tournament after his tee shot at 17 landed in thick rough left of the fairway about 162 yards from the pin. Haas then hit a perfect shot that skipped through the narrow opening to the green and rolled directly into the hole, briefly putting him into a tie with Langer and Sluman.
Langer has been the most efficient this week after posting consecutive rounds of 71 over the first two days. Hes also been the most consistent senior on tour this season, with two victories plus five top-10 finishes in 10 Champions Tour events this year.
Add to that, the 1993 Masters champion also showed hes capable of being competitive on the PGA Tour after finishing in a tie for 15th at The Players Championship earlier this month.
Haas led the tournament after an opening-round 69, and dropped slightly after a 72 on Friday. Hes already enjoying a solid season in which hes produced six top-10 finishes on the Champions Tour.
Sluman, who grew up in suburban Rochester, entered the tournament with an objective to simply make the cut after he failed to do so in his two previous times at Oak Hill during the 2003 PGA Championship and the 1989 U.S. Open. Now the 1988 PGA Championship winner is in contention to win on the course which hes played some 500 times.
Bruce Vaughan had a hole in one on the 164-yard No. 6'the same hole that produced four aces during the second round of the 1989 U.S. Open.