The 21-year-old remained unbeaten on 157, 40 runs more than what his team managed in the first innings after forging the match's first century-plus partnership with Dinesh Chandimal (42) to help the hosts take a handy 167-run lead with five wickets in hand.

Dhananjaya de Silva was batting on 24 as Sri Lanka erased the 86-run first innings deficit in the morning before dominating the post-lunch session, adding 137 runs at a run rate of over four for the loss of Chandimal's wicket.

Mendis brought up his maiden Test century in style, slog-sweeping spinner Steve O'Keefe over mid-wicket for a six, and his blooming sixth wicket partnership with de Silva is already worth 50.

The visitors' woes were compounded when spinner O'Keefe hobbled off the ground with Cricket Australia later confirming he has a "right hamstring issue" in a tweet.

Earlier, resuming on six for one, Sri Lanka received an early jolt with Mitchell Starch trapping Dimuth Karunaratne leg before for the second time in the match with the third delivery of the day.

O'Keefe dismissed Kaushal and spin partner Nathan Lyon sent back home captain Angelo Mathews (nine) to reduce Sri Lanka to 86-4. Mendis found an able ally in Chandimal who got a reprieve on 24 when a diving Starc failed to take a return catch.

Mitchell Marsh denied Chandimal his fifty but Mendis batted with consummate ease, sweeping the spinners and cutting the pacemen with equal confidence.

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