Ken Doherty and Fergal O'Brien both lost their first-round matches at the English Open, while world number one Judd Trump survived a scare in seeing off Louis Heathcote.
Doherty suffered a 4-1 defeat against China's Xu Si and Fergal O'Brien exited 4-2 to 2015 World champion Stuart Bingham.
Trump came from behind to beat Heathcote 4-3.
After a break of 75 helped Trump take the opening frame, Heathcote, ranked 69 in the world, had threatened an upset in Milton Keynes when two half-century clearances saw him move 3-1 ahead.
Trump, though, made the most of being allowed back to the table in the fifth frame with a run of 86 to reduce the arrears before levelling the match.
The 2019 world champion continued his momentum with another half-century break to take the deciding frame 73-5 and secure a place in round two.
Shaun Murphy, the 2005 world champion, edged out Robert Milkins 4-3 and Matthew Stevens saw off Jamie O'Neill 4-2. Jack Lisowski also triumphed 4-2 against Li Hang, while Luca Brecel beat Ian Burns 4-0.
Gary Wilson, the world number 19, beat Ukrainian Iulian Boiko 4-1; Welshman Ryan Day saw off amateur Mark Lloyd 4-0 and Swiss potter Alexander Ursenbacher recorded a 4-2 win over Scotland's Graeme Dott.
Earlier during Tuesday's afternoon session in Milton Keynes, 2020 world championship finalist Kyren Wilson beat Dominic Dale 4-2.
Wilson played on when needing snookers to take the decisive sixth frame by a point.
Tom Ford defeated Xiao Guodong 4-3 while Zhao Jianbo edged out Michael White by the same scoreline.
There were also wins for Matthew Selt, Nigel Bond, David Lilley and Simon Lichtenberg.
Trump 4-3 Heathcote— World Snooker Tour (@WeAreWST) October 13, 2020
The world number one overcomes a stern test to reach the second round of the https://t.co/0mCRoqdsmX English Open! 👊
A break of 61 in the last #HomeNations #EnglishOpen @judd147t pic.twitter.com/fHB9tgYTau
Earlier on Tuesday morning, Peter Lines had become the latest player forced to withdraw from the tournament in Milton Keynes after returning a positive coronavirus test.
Lines' son Oliver has also been forced to withdraw as a contact, despite testing negative for the virus prior to his first-round win over Noppon Saengkham.
Oliver Lines sarcastically described the decision as a "fair one" on Twitter, but government guidance says contacts of a positive case must self-isolate irrespective of any negative tests returned over the subsequent 48 hours.
Stuart Carrington had to withdraw after testing positive for the virus on Monday, along with Sam Craigie, with whom he had been in contact, and referee Andrew Barklam.
Both Craigie and Oliver Lines were scheduled to face Anthony McGill, who is now into the third round without having played a game.