Harris, whose previous career-high was 21 points last season against Akron while he was at Miami (OH), hit 8-of-12 from the field, including 4-of-7 from three-point. He added six rebounds. Forbes tallied his fifth 20-point game of the season and ninth of his career.
The Vikings fell to 4-4 this year, while Drexel, playing its second straight triple overtime game, improved to 5-2 and won its home opener.
Trailing 30-20 at halftime, the Vikings used 18 second half points from Harris and 12 from Forbes to rally and send the game into overtime.
The Dragons had a chance to win the game in regulation after Lewis split a pair of free throws to tie it at 58-58 with eight seconds left, but a runner in the lane by Frantz Massenat was off the mark.
Drexel took a six point lead (65-59) with two minutes left in the first overtime period, but a Lewis three-pointer and free throw by Harris brought the Vikings back within two points (65-63) with 1:21 to go. After a Drexel free throw, Forbes nailed a three-pointer to tie it at 66-66 and Massenat missed a three-pointer at the buzzer which would have won it for Drexel.
CSU assumed a four point lead in the second overtime period on two Lewis free throws with two minutes left, but Drexel cut the deficit to one (72-71) on a bucket and free throw. CSU missed a shot with 25 seconds to left, but Drexel knocked the ball out of bounds, keeping it with the Vikings. But a turnover and foul on CSU sent Massenat to the line where he split the pair with four seconds left, sending it into a third overtime.
It was CSU's first three overtime game since the 1993-94 season, when the Vikings went four overtimes with Kent State.
The teams traded baskets early, and a Forbes free throw gave the Vikings a 78-77 lead with 3:06 to play. But a 6-1 spurt by the Dragons gave Drexel an 83-79 lead with 16 seconds left.
Harris hit a 30-footer with eight seconds left to bring CSU back within one, but Massenat made both free throws on the other end to extend the lead back to three and Harris' desperation long three-pointer was off the mark at the buzzer.
Drexel took an early 7-4 lead, but buckets by Marlin Mason and Anton Grady gave the Vikings a one point lead (8-7) five minutes in. The Dragons responded by scoring eight of the next nine points to open up a six point advantage (15-9), but a Harris tip-in and two straight buckets by Sebastian Douglas evened the contest at 15-15 with 7:33 left in the half.
However, a 15-5 run by Drexel to close the half gave them a 30-20 lead at the intermission.
It was just the second time all season that CSU trailed at the half, the other time coming in the season opener against Iona.
The Vikings shot just 9-of-25 (.360) from the floor in the first half, but finished shooting 50-percent (29-58), including 10-of-21 (.476) from three-point.
Drexel shot 28-of-66 (.424) from the floor and held a 42-34 advantage on the glass. The Dragons also scored 42 points in the paint.
The Vikings are back in action on Saturday (Dec. 7) when CSU hosts Akron at 2:00 p.m. in the Wolstein Center.