Luka Doncic is clearly not happy. The Dallas Mavericks lost another close one on Monday as Devin Booker and the Phoenix Suns handed the Mavs their sixth straight defeat.

Luka was beside himself after missing a possible game-winner that would've broken the Mavs' current losing slump. Instead, the Mavs had to swallow another tough L as they continue to fall in the Western Conference early into the 2020-21 NBA season.

Watch Luka's angry reaction here at the end of another frustrating Mavs loss (via Bleacher Report):

The Mavs actually had a two-point lead prior to Phoenix's last possession. But with 10 seconds to go, the Suns drew up a great play that opened up Devin Booker. The brilliant Booker, who was struggling in the first half, drained a three with a second left on the game clock to put Phoenix up by one.

Doncic had one final chance to grab the lead back with a last-second heave but unfortunately, his long three was off to the right for the Mavs.

Phoenix was able to complete their two-game visit in Dallas with two huge wins which should explain Doncic's frustration. The 21-year-old Mavs superstar finished the game with a team-high of 25 points, five rebounds, and eight assists on another losing effort.

Josh Richardson also had a huge night for the Mavs in just his second game back after sitting out due to health and safety protocols with 24 points, five rebounds, four assists, and two steals.

It's back to the drawing board again for these struggling Mavs as they continue to take huge hits night in and night out. The good thing is they do have most of their guys back so hopefully, they get to build on some much-needed chemistry to get back on the winning column.