In his quarter-final against Djokovic he managed just a single game, but is confident it will be a different story here.
"I think Wawrinka was fantastic", said Cowan.
Murray won his quarterfinal match in four sets on Wednesday, while Wawrinka and Thiem each earned straight-sets victories. So I think he is getting more out of his game than most players. And Thiem then took the second set 6-3.
"He (Wawrinka) is playing great tennis".
He trails Murray in head-to-head meetings 10-7 and lost to the Briton in four sets in the semi-finals past year.
World number one Murray was the first British man in the Roland Garros final since Bunny Austin in 1937 when he finished runner-up to Novak Djokovic previous year. "I enjoyed it. But for sure when you win it's better".
Djokovic piled on the pressure when Thiem served at 4-5 and he had his man in trouble at 15-40. "He played good, but he was a bit nervous and tense", said Toni Nadal, who coached his nephew to 14 Grand Slam titles.
The three-set loss to Thiem, who will bid to reach his maiden grand slam final when he faces nine-time champion Rafael Nadal in the second semi-final on Friday (9 June), is the latest blotch on Djokovic's copybook since he completed the career grand slam 12 months ago.
Both held serve after that to take the set to a tense tie-break which Thiem won 7-5, Djokovic committing an unforced error on the second set-point.
Murray won the first set 7-6 (6).
And what about Andy Murray, who meets Wawrinka on Friday in a rematch of the 2016 French Open semifinals?
Wawrinka, attacking from the start, drew first blood in the eighth game, breaking with a forehand cross-court pass victor to punish Murray's tentative approach, but the Scot responded immediately, his brilliant defensive work repeatedly forcing Wawrinka to hit the extra ball.
Murray broke straight back to eventually force a tiebreak that featured a couple of scintillating exchanges that would be in the running for the "point of the tournament".
"He's played fantastic this tournament so far", Murray said of the 32-year-old, the oldest Roland Garros semifinalist since Jimmy Connors in 1985. You just shake off flu and rebound very quickly to the level you were before.
In the early stages, Murray had no answer to his opponent's exquisite ball striking from the back of the court, however - as he has reminded us many times before - Murray is a fighter and will not go down without a battle. This time it was Wawrinka's turn to defend stoutly, but Murray hit a thumping backhand cross-court victor on his third break point.
Serbia's Novak Djokovic gestures as he leaves the court after losing his tennis match against Austria's Dominic Thiem at the Roland Garros 2017 French Open on June 7, 2017 in Paris.
What makes this defeat more appalling is the fact that the 30-year-old had a flawless record of 5-0 against the sixth seeded Austrian Thiem before this match.
In the women's quarterfinals, No. 2 seed Karolina Pliskova defeated No. 28 Caroline Garcia 7-6 (3), 6-4.