Ronnie O'Sullivan shook off illness to defeat Neil Robertson and book his place in the semi-finals of the Dafabet Masters, where he'll meet Marco Fu, conqueror of Antrim man Mark Allen in the evening clash.

Defending champion O'Sullivan, seeking to win the tournament for a record seventh time, won the last four frames to seal a 6-3 success and delight his supporters at Alexandra Palace.

Robertson, who has featured in three of the last five Masters finals, started strongly and won the first frame with a break of 74 but O'Sullivan responded with a 63 to level the contest.

'The Rocket' went 2-1 up with a 51 but Robertson levelled and then knocked in breaks of 59 and 62 to win the fifth.

However, the Australian's resistance was broken by O'Sullivan, who - aided by breaks of 55, 54 and 68 - won the next four frames to make sure of his continued presence in the £600,000 event.

He said afterwards: "Physically I feel better. The last three or four days I've been really ill and this is the first day I actually feel better."

O'Sullivan was not at his best in defeating Liang Wenbo in the first round on Sunday, and he admitted after seeing off Robertson: "I've needed a bit of luck to get through.

"They're all tough matches but I just keep hanging in there. I felt I just dragged him down... but that's all you can do sometimes.

"I've had four or five years where I've been really consistent - hopefully I can turn it round.

"Maybe you miss easy balls as you get older and that's the difference between winning and losing but hopefully I've got three decent years in me."

On the prospect of a seventh Masters title, he added on BBC Two: "I don't think I'm playing well enough to win."

O'Sullivan will play Fu for a place in the final after the rejuvenated Hong Kong player defeated Allen 6-2 in Thursday's other quarter-final.

Breaks of 74 and 83 saw Fu open up a 2-0 lead, which he extended to 3-0 - only for Northern Ireland's Allen to cut the deficit to a single frame with runs of 70 and 54.

Fu regained control with a 97 and moved to within a frame of victory with a clearance of 140 - the top break in the tournament putting him in line for the £10,000 prize - before a 65 in the eighth frame took him over the line.