In other first round action, top seed Marin Cilic made a flying start to his bid for another strong grass-court campaign with a 6-3, 6-4 win over Spanish veteran Fernando Verdasco. "You start all over again".
"I feel good. My elbow is fine and I played three quality matches in Stuttgart".
Shapovalov was left to rue his failure to convert a set point in the opener as he bowed out against the man who ended Rafael Nadal's Wimbledon hopes previous year.
"It's going to be interesting, definitely". "The grass-court season, it's short but it's sweet as well".
Ranked unseasonably low at 261, the popular Swiss was ranked No3 in the world after he reached the final of the French Open last summer, but first-round losses at Queen's and then Wimbledon spelled trouble that would endure for the rest of the year and on into 2018. And he was in London practising a week before he played his first match against the fast-improving Briton Cam Norrie.
"Every day is getting better and in general I'm happy with my level", Wawrinka said.
Another American with a big serve is out, though, after sixth seed Jack Sock was beaten by Daniil Medvedev.
The 29-year-old Croat, champion at Queen's in 2012, lost only four points on serve during a 6-3 6-4 victory - his fourth in succession against Verdasco.
But as long as I can practice full, as long as I can put the hours on the court, as long as I can move well and put the work, it's positive.' Novak Djokovic recently said that the biggest challenge for Andy Murray is mental.
Murray is playing Nick Kyrgios in his first competitive match in 342 days, British number one Kyle Edmund is up against American Ryan Harrison and Evans, making his ATP Tour return following a drugs ban, faces Frenchman Adrian Mannarino.
The Russian prevailed 7-5 6-3 to increase his growing reputation.