Australia coach Darren Lehmann had said the top order batsman's place in the team for the Melbourne test, which starts on Saturday, was assured if he could prove he had recovered from a left hamstring strain.
Despite having missed Sydney Thunder's first outing of the season because of the injury, Khawaja scored a match-winning 109 off 70 balls and looked sharp in the field in a convincing runout at the Melbourne Cricket Ground (MCG) on Sunday.
"I'm really happy with the way it felt to be honest," Khawaja said in a televised interview after the one-run victory over the Melbourne Stars.
"The test was when I went back out on the field and how it felt backing up and it felt really good.
"The longer I was out there the more I started trusting my body. I was a little bit anxious at the start but the further along I got through the more happy I felt.
"I'm really happy with the start, I'll keep trying to tick all the boxes and keep trying to work on my body. Fingers crossed, I'll be right for the rest of the summer."
Khawaja was handed his third chance to establish himself in test cricket after a raft of retirements over the last 12 months left Australia low on experienced top order batsmen.
Taking the tricky berth at number three in the batting order, the stylish lefthander grasped his opportunity with both hands with 174 against New Zealand in Brisbane and an innings of 121 in the second test in Perth.
The hamstring injury forced him to sit out the inaugural day-night test in Adelaide, which secured the New Zealand series for Australia, as well as the thumping win in Hobart that began the three-match series against West Indies.
The 29-year-old is viewed as the long-term custodian of the "first drop" position for Australia so Shaun Marsh, who came in to replace Khawaja for the last two tests, looks likely to drop out of the team for the Boxing Day test.
Marsh will count himself unlucky after helping usher Australia to victory in Adelaide and scoring 182 in a world record fourth-wicket partnership of 449 with Adam Voges in Hobart.
(Reporting by Nick Mulvenney in Sydney, editing by Peter Rutherford)
