It was a tough Valentine's Day for Dallas Mavericks star Luka Doncic. The 21-year-old had another monster performance on Sunday against the Portland Trail Blazers, but it all went for naught after he missed an open triple that would've tied the game in crunch time.

Doncic, who tallied a game-high of 44 points, missed what would've been his sixth triple of the game with less than three seconds remaining and the Mavs trailing 121-118.

Here's Doncic's huge miss at the end of the game (via Bleacher Report):

Luka was wide open in the Mavs' last possession, as he got the ball with around five seconds left and literally no one near him to contest the shot. The ball bounced off the rim, which ultimately helped Damian Lillard and the Blazers seal their fourth win in a row.

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“I thought it was in. It went in and out, so I was disappointed, and that's on me. I should've made that shot,” the Mavs star said after the loss, via Callie Caplan of the Dallas Morning News.

Mavs head coach Rick Carlisle also echoed his young superstar's frustration. Luka Doncic had been lights out from distance, making 10 of his last 15 attempts before that crucial miss. Carlisle knows that Doncic wouldn't blow another golden opportunity like that if it happens again.

Frustrating has been a recurrent theme for the Mavs' 2020-21 season so far. They've failed to really get things going this season with a ton of health issues holding them back. These last few games, however, Dallas has looked a lot like last season's league-leading offense after winning their last four games coming into Sunday's home game against Portland. The loss now puts them at 13-15 as they continue to claw their way back to playoff contention.