The 23-year-old from Moratuwa bowled impressively to collect three wickets for 39 runs from his quota of 10 overs, as Sri Lanka narrowly failed to win the first of their three ODIs against Chris Gayle's side.
It brought to mind Muttiah Muralitharan, the Sri Lanka off-spin bowling legend, when he first stepped onto the international scene with his freakish bowling action.
Mendis trapped Gayle lbw with a delivery that went straight on, bamboozled Darren Sammy with a flipper that totally squared up the batsman and skidded through to hit the top of off-stump, before holding his nerve after Jerome Taylor clubbed him for six, tossing the next ball up having caught on the long-on boundary.
Even Ramnaresh Sarwan appeared clueless at times to what Mendis was delivering, and at one stage, after being deceived by the flight and the turn of a delivery, the West Indies vice-captain looked quizzically at the young spinner with an expression that seemed to suggest "what freak of nature have Sri Lanka unearthed now".
West Indies all-rounder Dwayne Bravo, who won Man-of-the-Match, had to agree that it was difficult to pick Mendis.
"To be honest, when we saw his stats - after 19 first-class matches, he had 111 wickets at an average of 14.54 - we knew he had to be bowling something good," Bravo said.
"Sarwan had problems picking him, and from the time we saw this, most of the batters retreated to the dressing room, and had a close look at his hand on the TV monitor.
"I actually went and had a look at his hand on the computer, and it was still really difficult to pick him, but I found that once you are prepared to watch the ball closely, it is half the job done."
Bravo admitted: "He is a very good bowler, and we will have to go back to drawing board to try to come up with a way to score off his bowling freely."
Sri Lanka coach Trevor Bayliss felt it was a pretty good debut effort from Mendis, and he too, believes he could have a long career in the game.
"I could tell you about his variations if I knew what they were, and even a lot of our guys struggle to know what he is doing with the ball," Bayliss quipped.
"The poise that he had in the first ODI - not just what he was bowling - to be able to keep a lid on things under pressure in ODI cricket is a very good sign.
"This has been the exceptional thing from my point of view. To be able to maintain his composure and do what he normally does was brilliant."
Bayliss agreed that ODIs was not the best place to experiment, and many coaches may have dissuaded Mendis from doing things his own way, but the Sri Lanka coach was prepared to let the young slow bowler let it all hang out.
"We just told him to go out there and do whatever he has done in the past," he said. "But it's how young players handle the pressure of international cricket that's critical, and he handled it very well.
"From my point of view, the higher up the ladder you go in this game, it's more of a mental thing. It's how you cope with pressure, and if something is working for him at one level, it's no reason why it cannot work at the next."
Bayliss believes the comparisons with Muralitharan will be inevitable, but for right now, he rejoices that he also has young slow bowlers of the quality of Mendis and leg-spinner Malinga Bandara at his disposal.
"Who knows, one day on one of those typical pitches in south Asia, we will pick all three," he said.
For the purists, this would be a delicious prospect.