Mark Selby established a convincing 6-2 lead over fellow three-time champion Mark Williams in their world championship quarter-final on Tuesday.

The Englishman won the first two frames without conceding a point, including a break of 121, and was 3-1 ahead at the mid-session interval in a best-of-25-frame match.

Williams, whose first pot was an extraordinary five-ball plant in the third frame, reduced the deficit with a break of 60.

The Welshman led 55-6 in the first frame after the interval but couldn't prevent Selby taking it before breaks of 90 and 76 extended his lead to 6-1.

But Williams finished the session with a fine break of 111.

Meanwhile, Anthony McGill came from 6-4 down to lead 2015 champion Stuart Bingham 9-7.

Early lead - Mark Selby
Early lead - Mark Selby AFP / Paul ELLIS

The Scot, who caused the shock of the tournament so far by knocking out defending champion Ronnie O'Sullivan, made breaks of 126, 83, 92, 130 and 75 to open up a two-frame advantage.

Kyren Wilson, last year's runner-up, also fought back to draw level at 8-8 with Neil Robertson.

Australia's Robertson, the 2010 champion, led 5-3 after the first session.

Wilson recovered to 6-6 before a break of 126 saw Robertson go ahead.

The Englishman won the next two frames but Robertson took the final frame of the day with a break of 66.

World number one Judd Trump and Shaun Murphy, both former world champions, are all square at 4-4, with seven of the frames featuring breaks of 67 or higher.