The Lions won the bruising encounter at Lang Park 23-21 but not without a huge scare after the Wallabies forwards won a penalty when their opponents collapsed the scrum under pressure in the final moments.
Wallabies replacement back Kurtley Beale missed the kick when he slipped during his follow-through, but the heart-stopping win did little to ease Rowntree's concern ahead of Saturday's all-important second test in Melbourne.
"There were some technical aspects I wasn't happy with," Rowntree told reporters at the Melbourne Rectangular Stadium on Monday.
"To be fair, the lads weren't happy coming straight off the field.
"I thought our work there, particularly as a tight five, was very good for 50 or so minutes but towards the end there were some critical, I would say pivotal moments.
"That nearly killed us that last scrum where we weren't in control, so technically we have to look at what we're doing there. Because that can't happen again. And the lads know that."
The Lions' tight five faces at least one forced change for the second test at Docklands Stadium, with lock Paul O'Connell ruled out for the rest of the series with a broken arm and set to be replaced by England's Geoff Parling.
Prop Alex Corbisiero is also under a cloud with a calf injury.
After dominating inferior, if willing, packs in the early tour matches, the Lions forwards struggled in the tourists' shock loss against the ACT Brumbies in Canberra last week and were on the back foot in the second half of the opening test.
Head coach Warren Gatland has named a strong pack for the tour match against Australia's Super Rugby strugglers Melbourne Rebels, with captain Dan Lydiate anchoring a powerful back row with number eight Toby Faletau and openside Sean O'Brien.
The Brumbies loss still stung for Rowntree, with the Lions' lineout a mess and the team thoroughly beaten at the breakdown, but it had at least prepared the team well for the highly physical first test, he said.
"That didn't go down very well, that loss. There were some stern words at halftime and afterwards as well," Rowntree added.
"A lot of the guys playing tomorrow night were involved in that.
"That's their chance to right those wrongs.
"(The Brumbies) gave us a real challenge and I think the breakdown challenges in that game set us up well for what came in the weekend."