Neil Robertson became the fifth world champion to be defeated in the opening round of this year's competition, joining Mark Selby, Graeme Dott, Shaun Murphy and Stuart Bingham in early departures home.
10-5 defeats for both Robertsons
The 2010 winner found himself 6-3 down overnight against world number 37 Robert Milkins and struggled to find his range when they returned to the table. Robertson squeezed the opening two frames of the day to give himself hope before losing four frames on the bounce, scoring just 36 points, as Milkins made breaks of 69, 55 and 54 on his way to a surprise 10-5 victory.
Yet there were no shocks when Mark Williams and Jimmy Robertson returned to the arena. Robertson pegged back the 2000 and 2003 world champion, taking the first two frames to reduce the deficit from 7-2 to 7-4. Yet Williams took advantage of a re-rack in frame 12 to contribute a 140 break before following it up in the next frame with another century. Robertson did pull back another frame but it was too little, too late as Williams cruised into a last 16 contest with Milkins.
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Higgins tested but looking strong
John Higgins became the third former world champion to qualify as he edged past Thepchaiya Un-Nooh 10-7. Higgins raced into a 4-1 lead with breaks of 62 and 51 before the Thai qualifier reduced the deficit to just one.
Yet Higgins found his range and won the next two with contributions of 104 and 59, missing out on a maximum in the former break. However, Un-Nooh hit back with three of the next four, including breaks of 121, 112 and 60, missing a chance of a 147 contribution of his own.
Unfortunately for the qualifier, that was as good as it got for the world number 58 as he succumbed to the quality of the four-time world champion. Breaks of 77 and 54 helped Higgins win a trio of the last four frames to progress into a last 16 contest with Jack Lisowski.
Trump and Day hold advantages
Just two first-round games are to be concluded with Judd Trump 6-3 ahead against Chris Wakelin in one of those ties. Trump contributed four breaks between 51 and 72 but is yet to hit top form against Wakelin who formulated 95, 69 and 141, the latter becoming the highest break of the tournament at that point.
Yet the feat was soon matched by Ryan Day in his contest with Anthony McGill. The world number 17 went 2-0 ahead, scoring 141 in frame two against the man ranked three places above him, before McGill made breaks of 65 and 75 to draw level. Day responded with 62 and 52, winning frame six by just one point.
The tight nature of the contest continued into the final few frames of the day as McGill won frame seven with a break of 51 by 15 points before Day edged a scrappy eighth on the final black after an earlier re-rack. The Welshman then ended the session with a new tournament-high break of 145 to give him a 6-3 lead overnight.
With the last 16 due to start on Thursday, fixtures look as follows:
Joe Perry  v Mark Allen 
Kyren Wilson  v Jamie Jones 
John Higgins  v Jack Lisowski 
Ricky Walden  v Judd Trump  / Chris Wakelin 
Ding Junhui  v Anthony McGill  / Ryan Day 
Lü Haotian  v Barry Hawkins 
Mark Williams  v Robert Milkins 
Ali Carter  v Ronnie O'Sullivan