Jack Taylor scored a game-high 43 points and went 11-for-23 from 3-point range for the Pioneers (4-6), who lost their third game in a row.
Simpson managed to slow down the run-and-gun offense of Grinnell, employing a 2-3 zone that yielded just 42 points in the second half. Simpson also won the battle on the boards, out-rebounding Grinnell 48-45.
Trailing 76-55 at the 14:16 mark in the second half, Simpson out-scored Grinnell 51-25 the rest of the way. Sam Amsbaugh's layup with 12:25 left sparked a 14-0 run that got Simpson back in the game.
A 3 by Nathan Balcom put Grinnell up 101-100 with 1:35 left, but Swain answered with the go-ahead layup. Taylor and Luke Yeager missed 3s and Swain knocked down a pair of free throws with 33 seconds left to give Simpson a three-point lead. Taylor missed two 3s on the next possession and Simpson avoided a near disaster after nearly throwing away the inbound with 3 seconds left.
Up Next: Simpson hosts Westminster (Mo.) on Wednesday, Dec. 17. Tipoff is set for 7 p.m.