Ronnie O'Sullivan struggled with his game as he fell behind in his Betfred.com World Championship quarter-final against Neil Robertson.
The three-time champion could not repeat the heavy-scoring form that earned him a standing ovation during the middle session of his second-round win over Mark Williams, and when Robertson pinched the final frame of the session to lead 5-3 it was a justified lead. The victory target in each quarter-final is 13 frames.
O'Sullivan had looked likely to make it 4-4 overnight but after reaching 58 he missed a red, using the rest, and when he returned to the table and failed to sink a blue it allowed his opponent in.
Robertson, winner in Sheffield two years ago, made a short run to 25 before returning to mop up blue, pink and black and clinch his two-frame advantage.
The standard of the contest was patchy, with both players producing flashes of brilliance but plenty of mediocre play too.
With Robertson a smart tactician, O'Sullivan allowed himself to be drawn into some exchanges when against other opponents he might have looked to dictate play. Robertson had breaks of 59, 58 and 100, while O'Sullivan also had a round century, 93 and a 58.
Fresh from beating Judd Trump on Monday, Ali Carter returned to seize a 5-3 lead over Welsh qualifier Jamie Jones.
Jones had a 92 as well as the highest break of the session with a stunning 127 in frame four. But the 24-year-old world number 36 from Cimla produced some messy play too, and when Essex man Carter fired in an eighth-frame break of 76, his fourth run above 50, it gave him a lead that was the least he deserved.
Stephen Hendry was attempting to battle his way back into his quarter-final after a miserable Tuesday morning display from the 43-year-old seven-time world champion saw him trail Stephen Maguire 7-1.
If Maguire were to win six of the eight frames the Scottish rivals are scheduled to play on Tuesday evening, it would mean Hendry suffering the indignity of defeat with a session to spare. On the other table, Ryan Day had breaks of 100 and 110 and led two-time runner-up Matthew Stevens 5-3 in an all-Welsh clash that was also resuming on Tuesday evening.