tee aces to take the tiebreaker.
Set two as well remained on serve as the players entered a second tie breaker.
Opelka revealed a smart serve and volley play to lead 5-3.
Then Tsitsipas double faulted trailing 4-6 to drop the set and level the match at one set all.
Tsitsipas, who had already been warned for receiving illegal coaching, then received another warning for racket abuse.
Serving down 2-3 deuce in the final set, Opelka struck a 115 miles per hour second serve ace out wide which he followed up with a down the line backhand volley winner to hold serve and level the set at 3 games all.
Opelka took a 30-40 lead in the Greek's following service game after two Tsitsipas double faults and an Opelka down the line backhand return winner.
Tsitsipas then framed a crosscourt backhand to drop his serve in the only break of serve of the day.
Tsitsipas in his anger struck a ball high into the stands which resulted in a code violation for ball abuse and a point penalty which sent Opelka ahead 6-7, 7-6, 4-3 15-0.
Opelka reached 5-3 following a fast hold of serve before Tsistsipas held serve at love to reach 5-4.
The 6 feet 11 inches tall American struck a down the line forehand volley winner and an overhead winner to reach 40-0 and match point before Tsitsipas netted a forehand return to end the match after two hours and 33 minutes of play.
The victory would be Opelka's first versus a top five ranked player.
In today's final, Opelka takes on the top seeded Daniil Medvedev of Russia at 1:00pm PST USA.