Opener Dimuth Karunaratne was rushed to hospital after a frightening blow by a bouncer on Saturday as Sri Lanka chased a massive Australian first innings total built on the back of three centuries.
In overcast conditions, the home team resumed day two of the second Test in Canberra on 384 for four and extended their lead to a massive 534 for five when skipper Tim Paine declared.
The impressive Kurtis Patterson was not out 114 and Paine on 45 at the declaration with Vishwa Fernando the pick of the Sri Lankan bowlers with 3-126.
At stumps, Sri Lanka were 123 for three in reply with Kusal Perera on 11 and Dhananjaya de Silva not out one.
Paine's declaration looked premature given the ease with which Sri Lanka's openers weathered the new-ball attack led by under-pressure Mitchell Starc.
On a flat Manuka Oval track Karunaratne and Lahiru Thirimanne saw off some lightning quick deliveries and a bouncer barrage and had built an 82-run stand before disaster struck.
Playing in his 58th Test, Karunaratne was 46 not out when a rising Pat Cummins ball glanced off his shoulder and onto his helmet, close to the neck area. He slumped to the ground, dropping his bat as Australian players ran to assist.
A doctor and physio sprinted onto the ground and called for more medics and after some 10 minutes, he was put on a stretcher and taken off the field on a golf buggy.
Cricket Australia said he complained of pain in the neck and tingling to the hands and was ferried to hospital.
Coach Chandika Hathurusingha said later he was in "good spirits" and "in no danger".
"It hit on the back of the neck so he is being assessed," he added.
It clearly unsettled Thirimanne who fell to spinner Nathan Lyon for 41 in the next over, caught by Usman Khawaja at slip. Cummins then clean-bowled Kusal Mendis for six and when captain Dinesh Chandimal gloved a Starc ball to Paine behind the stumps for 15, the tourists were in trouble.
SCORES IN BRIEF
AUSTRALIA: First innings 534 for 5 decl (Burns 180, Head 161, Patterson 114 not out, Paine 45 not out; Fernando 3-126)
SRI LANKA: First innings 123 for 3 (Karunaratne 46 rtd hurt, Thirimanne 41; Starc 1-32, Cummins 1-25)