The Tritons cut a 10-point lead down to one with 50 seconds remaining, but their comeback bid fell just short as James McCann's potential game-winner rimmed out on the final play.
Kyle Baxter finished with game-highs of 23 points and nine rebounds for Humboldt State, which improved to 12-4 overall and 8-4 in the California Collegiate Athletic Association with the win. The Lumberjacks have won five straight, including an impressive 65-61 triumph over league-leading Cal State San Bernardino on Friday night.
UCSD, which was coming off a hard-fought 63-62 victory over Sonoma State of its own, falls to 7-10 on the season and 3-9 in the CCAA. The Tritons had won two in a row prior to Saturday's setback.
"I was really proud of our effort in the second half tonight," head coach Chris Carlson said. "To fight and claw and scratch our way back and put ourselves in position to win it in the end, I was really pleased with that."
McGrath finished 5-of-12 from the floor, with all five of his field goals coming from behind the three-point line. He added five rebounds and two assists. Brue was 6-of-11 from the field and led the Tritons with eight rebounds, while McCann tallied 12 points on 4-of-9 shooting and dished out a game-high seven assists.
Baxter hit 11-of-19 from the field to lead three players in double figures for the Lumberjacks. Randy Hunter scored 16 points on 7-of-8 shooting, while Scott Clark chipped in with 10.
Humboldt State shot 46% (29-63) from the field overall, while UCSD finished at a 44% (24-54) clip. The Tritons finished 9-of-22 from the three-point line, 41%, after shooting just 3-of-11 from behind the arc in Friday's win over the Seawolves.
The Lumberjacks held a 37-31 edge on the glass and outscored the Tritons 42-26 in the paint.
Matt Lipski scored inside to put Humboldt on top 63-53 with 7:13 remaining, but UCSD refused to roll over, scoring 11 of the next 13 points to pull within one in the final minute. McGrath and McCann hit a pair of huge threes for the Tritons and, after a bucket by Hunter gave the Lumberjacks a 65-59 lead with 1:51 left to play, McGrath answered with two free throws to bring UCSD to within four.
After a crucial turnover by Clark, Mike Meza drilled a three from the left corner to cut the deficit to 65-64 with 50 seconds on the clock.
Bradon Sperling's layup missed the mark on HSU's next possession, leaving the door open for UCSD. After a timeout, McCann got into the teeth of the Lumberjack defense, but his runner was just off to the right. MacKenzie McCullough had a decent shot a last-second tip, but it came up short as time expired and the visitors escaped with the win.
"We like our chances when James gets a decent look inside the free throw line, it just didn't happen to go in," Carlson added.
Humboldt State held a 34-27 halftime lead and led by as many as 11 early in the second period. The Tritons cut the deficit to five on two separate occasions, but the Lumberjacks were able to hold them off until the big run at the end.
UCSD held HSU to just two points over the final seven minutes of play, but couldn't pull out the win.
The Tritons will travel to Cal Poly Pomona and San Francisco State next week to begin the second half of their CCAA slate. UCSD will square off with Pomona on Thursday, before facing SFSU on Saturday.