Usman Khawaja believes cricket's Decision Review System (DRS) has merit but ball-tracking technology is too easily bamboozled by swing and spin.

Khawaja was the batsman on the wrong end of a DRS verdict in the 2013 Ashes that was so bad it prompted Australia to seek clarification from the International Cricket Council.

That related to a caught-behind verdict that wasn't overturned. Khawaja's most recent innings served as a reminder of how the system has improved in that regard during the past three years.

The first drop was out for a golden duck at the WACA against South Africa but successfully reviewed the caught-behind shout and stayed at the crease.


"I knew I didn't hit it so it worked in that instance," Khawaja said, having gone on to score 97.

But Khawaja was also in the middle when Mitch Marsh was controversially given his marching orders on day five.

South Africa successfully reviewed an lbw shout from Kagiso Rabada, with the ball-tracking replay suggesting the reverse-swinging Kookaburra would have clipped leg stump.

Skipper Steve Smith joked the verdict showed Rabada had started to bowl leg spin, while Khawaja questioned the accuracy of the ball-tracking replay long before Michael Clarke, Mitchell Johnson and Mark Waugh did.

"I knew there was something not right. I walked straight up to (umpire) Aleem Dar and said 'look, the contact point of where it actually hit and where HawkEye is saying it hit is just off'," Khawaja told radio station FIVEaa.

"The South Africans were as surprised as anyone that was given out. I walked past a couple of them and you can always tell when they're being sheepish and they know they've got one away."

Khawaja added it wasn't the first time a ball-tracking replay had delivered a surprising reading.

"I've had an issue with ball tracking, even in places like Sri Lanka and India where the ball spins a fair bit," he said.

"I don't think the ball accounts for the spin and swing really as well as we know what it does.

"It doesn't just happen against us. I'm sure we've got a couple that have been a bit dicey, you always remember the ones that go against you."