Neil Robertson failed to back up his recent Masters title as he was knocked out of the German Masters in the first round against Ricky Waldren.
Robertson will be especially disappointed given he led 3-2 only to see Waldren reel off breaks of 71, 79, and 124 to turn the match on its head.
Asked how much of a boost claiming a big scalp could give him, the Englishman told the World Snooker Tour's official Twitter account: "They're the hardest games, to be honest, because you're playing someone in top form, obviously a seed on the TV table where they're more at home, if you like.
"It's a difficult hurdle to overcome and you've got to just stick in there, so to get that win can give you a good springboard."
Stephen Maguire got off to the perfect start in his match against Tom Ford when he rattled in 135 to take the first frame, but managed only eight more points in the next four as he slipped to a 5-2 defeat.
Back-to-back breaks of 76, 88, 53 and 81 put Ford firmly in the driving seat and although the Scot reduced the deficit to 4-2, he clinched victory and a second-round clash with Zhao Xintong with a visit of 104.
Craig Steadman beat Michael Georgiou 5-2 to set up a meeting with Kyren Wilson.
During the afternoon session, world number eight Mark Williams was dumped out of the tournament after going down 5-3 to Zhao.
The pair were locked together at 3-3 when the Chinese player put together breaks of 89 and 70 to progress.
Visits of 129 and 120 laid the foundation for Brecel's 5-3 victory over Zhang Anda, while Wilson rounded off a comprehensive 5-1 win against Jimmy Robertson with breaks of 94 and 117.
Zhou Yuelong beat Anthony McGill 5-2 to book a second round date with reigning champion Judd Trump.