Clarkson opened ECAC Hockey play Friday night with a 4-1 win over Renssselaer before 2,550 fans at Cheel Arena.
The Engineers struck first, scoring on a power play with a shot from Ryan Haggerty at 18 minutes, 6 seconds of the first period.
But Clarkson (6-1-2 overall) answered back when Corey Tamblyn scored on a slap shot from behind the circles with just 8.9 seconds remaining in the period to tie the game 1-1.
Louke Oakley gave Clarkson the lead for good with a goal at 8:43 of the second period.
Tamblyn scored another goal, this one on a power play at 14:05 of the third period to make it 3-1.
Nick Tremblay ended the scoring with an empty-net goal at 17:02. RPI fell to 1-7 overall.
Clarkson coach Casey Jones