Defending champion Neil Robertson fell to a surprise 4-2 loss to Jimmy Michie in his first group match at the Royal London Watches Grand Prix in Aberdeen.
Robertson bounced back after losing his first match
The Australian dug deep in his next match to beat Mark Davis 4-2 and keep alive his hopes of making the last 16.
Ronnie O'Sullivan, the 2004 champion, eased to a 4-0 whitewash over Walsall qualifier Mark Joyce in his first game.
"The Rocket" then had to come back from 3-1 down to beat Leicester's Tom Ford 4-3 in his next match.
O'Sullivan compiled breaks of 50, 70 and 72 to start his campaign with a comprehensive victory.
He looked set for another straightforward win when he opened with a 123 break against Ford.
But the underdog responded by winning the next three frames and O'Sullivan rattled in breaks of 100 and 119 to level, before taking the deciding frame.
"I was pleased with how I played, my preparations for the tournament have been all right," said O'Sullivan.
Robertson now faces group matches against Joe Perry, former Welsh Open runner-up Stephen Lee and Belfast's Joe Swail.
"I'm very disappointed to have lost my first match, but I lost my first match here last season, so maybe it's a good omen," said Robertson.
Meanwhile, UK champion Peter Ebdon was forced to battle back from 3-0 behind to beat Chinese prospect Liu Song 4-3 in his opening match.
Ebdon then grabbed another final-frame 4-3 win over Dubliner Joe Delaney.
Mark Selby was upset 4-2 by veteran Dave Harold in his first match, while former world champion Shaun Murphy wasted no time in racing to a 4-0 victory over qualifier Ben Woollaston.
Murphy then trailed Stuart Pettman before hitting back with breaks of 59, 55 and 70 to maintain his excellent start to this year's £470,500 event.
Six-time world champion Steve Davis started his campaign with a 4-0 defeat at the hands of Gerard Greene.
And Ding Junhui - already a three-time ranking event winner at 20 - slumped to successive defeats.
The Chinese prodigy was beaten 4-1 by both Hong Kong's Marco Fu and Essex's Stuart Bingham.