Tannan Peters and Bruce Grimm Jr. produced timely shots as two free throws from Lee Ross iced the shootout in Grace’s favor.
Neither team could be slowed down on the offensive end in the first half as the sides combined for 86 first-half points.
Robert Morris maintained a small lead for much of the first period and led 41-35 with two minutes remaining. But Grimm, Elliot Smith and Greg Miller ended the half with 10 straight points for Grace to give the Lancers (3-1) a four-point cushion at the break.
The second half featured eight ties and eight lead changes. A 7-0 spurt from the Lancers gave Grace a lead with eight minutes to play, and they managed to hold onto their advantage until the final two minutes.
The Eagles (2-4) went on a 9-2 run to go ahead 86-85 with 1:46 remaining, but the Lancers countered with a basket from Peters on their next possession.
Robert Morris tied the game with a single free throw, and Grimm sank two free throws on the other end of the court as Grace led 89-87.
The Eagles tied the score again with a layup with less than 30 seconds remaining, and Grace hustled down the court where Grimm made a short pull-up jumper with 17 seconds left on the clock.
Robert Morris’s Larry Dumas, who scored 43 points in defeat, missed a contested 3-pointer with five seconds to play, and Ross was fouled for the Lancers. He calmly sank both free throw attempts to seal the upset.
Four players reached double-digit scoring for Grace, including a 28-point, 11-assist performance from Grimm.
Miller just missed his fourth double-double of the season with 21 points, nine rebounds, three blocks and three steals, and Smith made 3-of-5 from beyond the arc for 17 points.
Peters tallied 11 points and three assists, and Ross had six points and five boards off the bench.
Overall, Grace connected on 55 percent of their shots, including 59 percent (13-of-22) in the second half. They tallied 18 assists on 28 made field goals.
The Lancers will kick off the Crossroads League season on Tuesday with a home game against Mount Vernon Nazarene at 7 p.m.