Leishman is the best of the four Australians in the field at 7-under and trailing Sharma by 6 shots but, more importantly, there are 10 players between him and top spot.
Leishman has been consistent in his debut appearance at Club de Golf Chapultepec recording scores of 69-68-69 but it is Sharma who has been the revelation of the tournament.
The 21-year-old is already a two-time winner on the European Tour this season but the step up in class to the WGC level seems to have done little to bother him.
The surprise 36-hole leader, Sharma continued to baffle most by maintaining his overnight buffer of two shots with a superb round of golf including a gutsy 13 foot par putt at the final hole.
A birdie at the short par-4 first suggested there was little in the way of nerves and he backed up with another at the third.
A birdie and a bogey on the way to the turn saw his lead at four shots though he wasnâ€™t without challengers as several players went low.
Starting well back of the lead Justin Thomas showed what could be done with a brilliant 9-under 62 while Englandâ€™s Tyrrell Hatton also found his rhythm in a 7-under 64 to get within two of the lead and a share of second place.
American Pat Perez was also threatening from in front when he briefly joined the lead with his seventh birdie of the day at the 14th but a bogey-double bogey run at 16 and 17 saw him quickly slide back down the standings.
Sharma now faces the biggest test of his short career as he heads to the final round with the likes of Phil Mickelson and Sergio Garcia hot on his heels.
69-68-65-March 3, 2018
Also sharing second is Rafa Cabrera-bello whose 2-under 69 kept him in touch while Xander Schauffele dropped off the pace ith a 1-under 70 to be T6 and three behind. Adam Bland is next best of the Australians at 5-under and T21 after a disappointing finish to his round.
The likeable left hander was 1-under at the turn with two birdies and a bogey to be and around the top 10 but finished even par for the day after two back nine bogeys and a birdie.
Wade Ormsby posted his second sub-par round of the week after his opening 79, a 2-under 69 moving him to 2-over for the tournament and a share of 46th place.
Brett Rumford signed for his best score of the week, a 1-over 72, to be 11-over for the week and remain near the tail of the field.
SIGNATURE HOLES - 7TH AT BAYVIEW GC, SYDNEY:
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