Neil Robertson established a narrow 5-3 lead over John Higgins in a fiercely contested opening to their quarter-final. Higgins compiled breaks of 61 and 56 to take the first frame and the fourth to draw level at 2-2. However, the emotional and physical toll of defeating Ronnie O'Sullivan 13-12 in an all-time Crucible classic on Monday appeared to weigh on the 50-year-old Scot at times. The four-time champion made six unforced errors before reaching the mid-session interval and was far from his best in a scrappy affair. Australia's Robertson, who won the world title in 2010, also failed to hit the heights despite enjoying runs of 77 and 70 and, at one point, he even had to have his chair repaired, adding to the protracted nature of their contest. While he took the final two frames of the session, his pragmatic approach and an unfortunate run of the balls contributed to a drawn-out eighth frame that lasted almost 52 minutes and delayed the start of the evening session.…