At the interval, opener Wasim Jaffer (19) and Vinit Indulkar (6) were at the crease. The batsman to fall in the Mumbai reply was opener Vinayak Mane who was dismissed by Glenn McGrath for 3.
Earlier, the Aussies, 282 for 6 at lunch, applied closure to their innings at the fall of their seventh wicket, Brett Lee. The tearaway pacer was caught by Vinit Indulkar off Ramesh Powar, the short and stocky Mumbai off spinner, after having added 54 runs in only 59 minutes with captain Adam Gilchrist.
The left-handed Gilchrist, who looked a bit suspect against the Mumbai spin bowling initially, later opened out and smashed two sixes, both over the straight field, and one four while making an unbeaten 42 in his characteristic attacking style in 91 minutes and off just 76 balls.
The renowned Australian pace duo of Glenn McGrath and Lee then had a go at the home team's openers with fast and accurate stuff that was negotiated well by Mumbai openers Wasim Jaffer and Vinayak Mane.
But the latter finally fell to the bait of short ball from the gangling McGrath and put up a tame catch to square-leg fielder Cameron White, substituting for Damien Martyn who had earlier retired to the pavilion after making a classy 71.
Martyn was reported to be down with a stomach bug by Media Manager Jonathan Rose and did not take the field after lunch.
The Aussies preferred to give long spells to McGrath and Lee to get them used to the heat and wicket conditions in the sub-continent. The gangling McGrath bowled a pretty impressive spell of six overs for three runs and a grabbed a wicket while Lee had two spells, from either end of the ground, and bowled fast and straight mostly.
For the Mumbai batsmen it was basically a question of blunting the Aussie pace attack and Jaffer looked quite composed. He hardly flirted with a ball not on the stumps and stayed put at the crease for 83 minutes in which he faced 63 balls and hit only one four.
Indulkar, making his first class debut, was troubled by McGrath's mix of short pitched balls, slower ones and yorkers, survived a few close leg before shouts from the bowler to remain unbeaten at the end of the second session of play.
Play, which was extended by half an hour before lunch to make up for lost time due to the inclement weather yesterday, is to continue for two and a half hours in the last session too.