Wawrinka was going for his 17th career title and second in Rotterdam, after winning in 2015.
"Stan is a part of this win. You're my brother", he told his Swiss opponent. "It's good to see that I can keep being there, mentally, physically". "Was a good week for you too, and I hope we have many more battles".
It had been nearly two years since three-time Major champion and 2015 Rotterdam titlist Stan Wawrinka reached a final.
Shapovalov recovered from 15/40 in his second service game, but Wawrinka finally gained the break with a trademark backhand victor to take a 5-4 advantage. "It's my first final since the surgery, so to show I can still play at this level against the top players is very important for me".
"I played four good matches here, I kept my level up all week".
Three-time major champion Stan Wawrinka's rebuilt knee couldn't quite carry him to the title in Rotterdam on Sunday.
"I was able to play a great match and was always focused".
The Swiss world number 68 sent a stinging service return victor down the line to clinch victory, which comes nearly a year and a half after he underwent two knee surgeries in the summer of 2017.
Wawrinka is into his first final in nearly two years.
Monfils revealed that he has been suffering all week with a left wrist injury. "I'm just happy I managed to win today".
"But when I hit as hard as I could with the backhand - "ohhh", he said in reference to the wrist pain he was feeling. "I followed the game plan from the beginning to the end", the 26-year-old Italian said.
He then had two further break-point opportunities in the fifth game before he broke Wawrinka's serve for the second time to seal the set 6-3.
Third seed Marco Cecchinato wrapped up a dominant week in Buenos Aires with a 6-1 6-2 win over Diego Schwartzmann to win the Argentina Open.
The big-serving 21-year-old wasted two match points in a second-set tie-break as Schnur - who had not won a main draw match on the Tour until this week - forced a decider.
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