Pat Cummins' "dream ball" to remove Pakistan star Babar Azam has put Australia on track to retain the Benaud-Qadir trophy at the MCG.

With the tourists enjoying a rare period of dominance in Australia, captain Cummins again stepped up when his country needed him late on day two of the Boxing Day Test.

The 30-year-old changed the second Test in three overs when he removed opener Abdullah Shafique (62) and Azam (one) to trigger a mini-collapse.

Cummins held onto a stunning return catch to get rid of Shafique, but his dismissal of Babar will go down as one of his favourite 245 Test wickets.

Babar, one of the world's premier batters, lost his wicket after receiving an unplayable delivery from the Australia quick that hit the seam and clipped the top of middle stump.

"It's a dream ball," Cummins recalled.

"It's what you try to bowl most balls, but it's rare that it comes off so really happy with that one.

"The wicket feels like it's got a little bit in it if you get it in the right areas."

Pakistan took the points from the first two sessions on day two, but will now need something special to avoid losing a 16th-straight Test in Australia and going down 2-0 in the three-match series.

But Australia will need to improve their over-rate to avoid being docked more points in the World Test Championship.

In the corresponding Test against India three years ago, Australia received a penalty for not bowling their overs quick enough that ultimately cost them a spot in the 2021 WTC final.

Cummins' team has already lost 10 points in the current WTC standings after being tardy with their overs during the Ashes.

"You keep an eye on it," Cummins said.

"I think we got about three or four minutes back, we were 13 minutes down at one stage, I think we're nine or 10 now.

"Keep half an eye on it, and if it starts getting tight start trying to make sure you can rein it in, always try and not waste too much time, if we can."