Sexton had been out with hamstring trouble and the Guinness PRO12 side were keen not to overwork the fly-half as he returned to action.
Nacewa took over the kicking duties in last week's win and continued to take responsibility off the tee.
"Look, he's coming into his first European game; him and Sean O'Brien," Nacewa said.
"It's a team effort and I kicked well in the Captain's Run so I just got the charge.
"I was kicking last week (against Castres) and I came down here yesterday at the Captain's Run and just started slotting them, kicking them well.
"So, even before kick-off I knew I was going to take the kicks. It was happy days and it went well today."
Nacewa was 100% throughout the match notching four from four at the Altrad Stadium. His three penalties were all Leinster had to show for their efforts heading into the 80th minute and it looked as if they would be returning to Dublin with nothing.
However, with Montpellier 22-9 up, Nacewa latched onto a pass from Jamison Gibson-Park down the left and scampered under the posts to make the conversion easier for himself and ensure Leinster salvaged a losing bonus point to stay top of Pool 4.
Leinster now have back-to-back games against Northampton Saints in December - visiting Franklins Gardens on the 9th December before hosting them at the Aviva Stadium a week later.
"This competition is so hard and every single point counts, especially in these early two rounds" said the captain.
"It's a great sign by the squad and more so the bench; the impact those guys had there to come back there at the end and come away from there with the point."
Leinster will resume Guinness PRO12 action on Saturday when take on Connacht at the RDS in a repeat of last year's final when the men from Galway ran out comprehensive victors.
Guinness PRO12 Final 2017 Ticket Information: Fans can save up to 20% on selected tickets, and prices start at just €30 adults and €5 child, and be booked via www.ticketmaster.ie. For further information visit http://www.pro12rugby.com/final
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