What it means: Karlsson was the first to break free from the pack at 4 under, but he was later passed by Molinari, who finished T-2 last week at the Open de Espana. The Italian closed his round in style to grab sole possession of the lead, six clear of world No. 1 Rory McIlroy.
Round of the day: Molinari made it around Wentworth without dropping a shot, turning in 2-under 33 before heating up on the inward half. He added three birdies in a four-hole stretch from Nos. 11-14 before birdies on Nos. 17 and 18. He birdied each of the four par-5 holes during his opening round.
Best of the rest: Karlsson made six birdies against just one bogey to put himself in the early mix with a 67. The lanky Swede missed only two fairways on the day and took just 26 putts en route to his lowest round on the European Tour since the opening round in Abu Dhabi in January.
Biggest disappointment: Graeme McDowell has missed each of his last three cuts at Wentworth, and that streak may continue after an opening 74. McDowell played his first three holes in 3 over en route to an outward nine of 38, and the Ulsterman circled only three birdies on the day.
Main storyline heading into Friday: This event hasn't been kind to first-round leaders, as only five of 60 have gone on to win. Still, weeks after being the last man into the field at the WGC-Cadillac Match Play Championship, Molinari sits two shots clear of the field as he looks to win for the first time since 2012.
Shot of the day: Andy Johnston offered the best celebration of the day after a hole-in-one on No. 10. Johnston hit an 8-iron from 151 yards, and while he still shot 5-over 77, the ace did earn him a new BMW M4.
Quote of the day: "I could feel myself getting a little angry out there." - McIlroy, after opening with a 1-under 71.