SHEFFIELD, England - China's top snooker player Ding Junhui delivered a break of 100 but still trailed Ryan Day 5-4 temporarily in the first round of the 2012 world championship on Tuesday.

The 25-year-old Chinese, who is one of the favorites for this tournament having reached the semifinals last year, dominated the first frame with a break of 63 before Welshman Day levelled it.

Welsh Open champion Ding restored his advantage with a break of 47 before Day, 32, again drew level at 2-2.

Ding, who won all their previous four meets before Tuesday's clash, whitewashed the world No. 35 by knocking in a break of 100 to regain the lead.

However, Day took a scrappy sixth frame and won the next two to guarantee himself a lead to take into Wednesday's concluding session before Ding narrowed the gap to only one as he clinched the last with a break of 53.

China's world No. 10 has so far collected the titles of Masters and UK championship, which were tipped as the "big three" events of a snooker season along with the ongoing championship.

If Ding can overtake the lead and beat his opponent under the best of 19 frames, he will meet compatriot Cao Yupeng in the last 16 after the Crucible debutant upset Mark Allen 10-6 on April 22.

Judd Trump, who beat Ding in last year's semifinal, took a 5-4 lead of Dominic Dale after the first session started in the morning.

The 2011 world runner-up battled hard not only against his opponent, but also a suspected dose of food poisoning as he looked unwell in the match.

Joe Perry, the world No. 26 will take an 8-1 lead into Wednesday's second half after dominating his first session against former world champion Graeme Dott in the afternoon.

Elsewhere, another last-16 berth was grabbed by Ronnie O'Sullivan.

Having established an impressive 7-2 lead in Monday's first session, the three-time world champion only needed to win three more frames to beat the reigning China Open champion Peter Ebdon.

The Rocket finally wrapped up a convincing 10-4 victory on Tuesday's afternoon to chase a fourth Crucible title. He will face Mark Williams or Liu Chuang of China in the next round.