Dustin Johnson hit a flawless nine-under-par second round to storm into the lead at the Saudi International.
The world no. 3 profited from calm conditions at the Royal Greens Golf & Country Club Friday morning, converting seven birdies and an eagle to build a three-shot advantage.
Johnson set the tone for a fine round with early birdies on the 11th and 12th as he set about eating into the advantage held by overnight leader Thomas Pieters.
He gained two more shots at the 15th and 18th, but found himself behind Lombard who motored into a two-shot lead at the turn.
The South African followed up a birdie at the 17th with a brilliant eagle at the 18th, then hit consecutive birdies on the 1st and 2nd to heap pressure on the field.
But Johnson responded, hitting birdie at the 2nd as Lombard dropped a shot on the last.
Johnson took the lead for the first time at the 4th with a beautiful eagle putt from 30 feet out on the fringe, then holed successive birdies on the 6th and 7th to increase his lead and finish on -11 at the end of Day Two.
Li kept himself in contention with birdies at the 11th and 13th before holing two wonderful long putts from 25 and 35-feet on the 2nd and 3rd respectively.
He dropped a shot on the tricky 4th but came back with birdies at the 7th and 9th to finish on -8 alongside Lombard.
Alexander Levy of France, Richard Sterne of South Africa, Ryan Fox of New Zealand and Chris Paisley of England are tied for sixth on -6, while Ian Poulter is one shot back on -5 and in-form American Bryson DeChambeau is at -4.