Moroccan Amine Ahouda produced a big upset against Marcel Granollers in his homeland at the Grand Prix Hassan II, while last year's runner-up Borna Coric eased through to the second round despite an embarrassing error.
World number 946 Ahouda claimed the biggest upset of the season, judged on rankings, by defeating the eighth seed 6-4 6-4 in Marrakech on Tuesday
The 19-year-old Moroccan, playing only his second ATP match, defied the odds to send the Spaniard - ranked 901 places above him - and eighth seed packing.
Ahouda broke once in the first set and three times in the second to secure his place in round two on a memorable day for the teenager, who was buoyed by beating Mikelis Libietis in his country's Davis Cup defeat to Latvia at the weekend.
"This was a very good match for me," said Ahouda. "I felt confident after Davis Cup. Granollers is a great player and this victory means a lot to me.
"I'm living my dream and want to continue playing well. This is a great victory, but I want to keep going match by match. Hopefully I can continue as I love playing in front of the Moroccan crowd."
Coric, beaten by Federico Delbonis in the final 12 months ago, advanced to round two with a 6-3 6-2 victory over seventh seed Diego Schwartzman.
The 20-year-old was left red-faced when he prodded what ought to have been a simple forehand winner into the net, but saw the funny side of it.
Easier to laugh this off after a win :) The minute I did I knew it was gonna be all over the social media by the time I get off court :) https://t.co/Zfwr7AeVRW-- borna coric (@borna_coric) April 11, 2017
Oh Tuesdays...pic.twitter.com/WV834TfYzo-- Tennis TV (@TennisTV) April 11, 2017
He retweeted a video of the shot and posted: "Easier to laugh this off after a win ... The minute I did I knew it was gonna [sic] be all over the social media by the time I get off court."
Coric will now face wildcard Reda El Amrani, who was 7-6 (7-3) 1-0 up when defending champion Delbonis retired due to injury, while Gianluigi Quinzi beat Paul-Henri Mathieu.