Ronnie O’Sullivan missed a chance to turn up the heat on Mark Selby as humidity threatened to wreak havoc in the first session of their world championship semi-final at the Crucible in Sheffield. O’Sullivan complained about the worst kicks of his career after an error-strewn start to the session, which he edged 5-3 despite dominating his out-of-sorts opponent. After both players suffered a series of bad cue ball contacts in the third frame, the 44-year-old O’Sullivan told referee Paul Collier: “I’ve never had kicks like that before in my life.” Officials took the unusual step of changing the balls during the mid-session interval and the kicks appeared to subside, with O’Sullivan fashioning an overnight advantage that ought to have been more comprehensive. Players and pundits, including the six-times world championship runner-up Jimmy White, have suggested the warm weather may be a factor in the increased incidences of contact problems. White said on Eurosport that “it might be the humidity outside”, while O’Sullivan himself referenced the “damp conditions” after his second-round win over Ding Junhui. A World Snooker Tour spokesman confirmed that “humidity is bound to be a factor”, but pointed out that kicks have been “dramatically reduced” in recent years following the introduction of an anti-static cloth. O’Sullivan had been the first to suffer in the opening frame when a bad contact on a black brought his break of 59 to an end, although a brilliant long red belatedly helped him nudge ahead. Both players made uncharacteristic errors in the following frame, with Selby’s proving the most costly when he caught a red on the lip of the pocket on a break of 39, and some fine long-potting from O’Sullivan helped him extend his lead. Selby held on to win a near-farcical third frame in which the three-times champion was seen to express his frustration, and after which O’Sullivan engaged Collier in conversation as his opponent briefly left the arena. O’Sullivan went 3-1 ahead with a break of 85 before the interval, and while the kicks proved negligible upon the resumption, the errors continued as Selby missed the simplest of greens to help sweep O’Sullivan into a 4-1 lead. However, Selby responded in combative fashion by winning a sixth frame that hinged on his potting of a red to the middle which O’Sullivan had earlier refused. O’Sullivan fired a break of 58 to go 5-2 ahead but Selby clawed his way back from a 51-point deficit in the final frame of the evening to finish a largely forgettable session 5-3 behind. Anthony McGill moved closer to a first world final by opening up a 6-2 lead in the opening session against the eighth seed Kyren Wilson. Wilson was almost unrecognisable from the player who polished off the defending champion Judd Trump on Tuesday as a series of missed pots and safety errors gifted qualifier McGill the chance to continue his dream run in the tournament. After an epic first-round triumph over the 13th seed Jack Lisowski and successes against Jamie Clarke and Kurt Maflin, McGill now stands a strong chance of joining Stephen Hendry, John Higgins and Graeme Dott as the only Scottish finalists in the Crucible era.