Battling Allen makes dramatic departure on day of surprises
It was a day of shocks at the World Grand Prix in Preston as Antrim's Mark Allen joined Ronnie O'Sullivan in exiting the £300,000 ranking tournament.
Allen was involved in a gripping last 16 tussle with China's Liang Wenbo that went all the way.
Liang was 2-1 up when the Chinese star and the Pistol began to trade a series of big breaks. Allen made 95 to restore parity, but was immediately on the back foot once more when Liang made a contribution of 85 in the next.
Allen ensured a decider with runs of 67 and 61 but Liang held his nerve to win.
Meanwhile Robertson gained revenge for his recent defeat at the Masters to comfortably see off O'Sullivan 4-1.
The Thunder from Down Under stamped his authority from the off, making breaks of 80, 70 and 43 to storm to a 3-0 advantage.
That took him within one frame of inflicting a first whitewash defeat on O'Sullivan in a full ranking event since the 2006 China Open against James Wattana.
However, the five-time World Champion managed to get on the scoreboard, winning the fourth frame on the final pink.
Robertson wasn't to be denied and charged to the line with a break of 83 to secure victory.
"I worked really hard on the practice table yesterday evening and put a lot of things right," said Robertson.
"I was full of confidence, knowing in myself that I was going to be playing very well. That was one of the better performances I've had against Ronnie.
"There wasn't a lot he could have done about the result. My safety was fantastic and long potting very good. It was probably the performance of the season so far for me."
Judd Trump also fell at the last 16 hurdle going down to the in-form Barry Hawkins 4-1, while Shaun Murphy just edged out Ding Junhui in a 4-3 thriller.
Hawkins' good run continued last night when he booked the first semi-final place with a 4-2 victory over Robertson.