The "Greek Freak" also recorded a triple double in the 117-111 win Thursday at Toyota Center in Houston. Antetokounmpo logged 30 points, 13 rebounds and 11 assists in the victory.
His block came with nine minutes remaining in the third quarter. The Rockets led 71-56 when Harden took off on a breakaway. The 2017-2018 NBA MVP sprinted down the court before reaching the paint and picking up his dribble. Harden floated toward the rim while defended by 7-foot center Brook Lopez. Harden tossed a shot over Lopez, but did not see the "Greek Freak" trailing the play.
The 2018-2019 NBA MVP came flying in and used his right hand to swat the ball away from the rim.
"James Harden is one of the best players to play this game and one of the best offensive players in the league," Antetokounmpo told reporters. "We just tried to make him drive the ball and make a pass. The less shots he takes, the better for us.
"He had a tough night. Guys like that are going to get 20 shots up. We have to just have to make it as tough as possible and make his teammates make plays, not him."
Harden had 19 points, 14 assists, seven rebounds and seven turnovers in the loss. Russell Westbrook led the Rockets with 24 points. Westbrook also had 16 rebounds and seven assists in his first game with the team after being acquired in an offseason trade from the Oklahoma City Thunder.
"I didn't play well offensively this entire night," Harden said. "Give them credit ... but this one is on me. I wasn't aggressive enough and that's what it was."
The Bucks host the Miami Heat at 5 p.m. EDT Saturday at Fiserv Forum in Milwaukee. The Rockets host the New Orleans Pelicans at 8 p.m. EDT Saturday at Toyota Center.