O'Gara has notched a record-breaking 1,075 points in 121 caps for Ireland but was overlooked in favour of Sexton in Declan Kidney's starting XV for the recent RBS 6 Nations campaign.
Sexton continued to get the better of his rival with the Leinster man kicking three penalties to O'Gara's one in the first-half.
O'Gara levelled the scores with a pair of penalties after the break but Sexton restored Leinster's lead before replacements Fergus McFadden and Ian Madigan sealed the win with another penalty and a drop goal.
Meanwhile, Wales second-row Alun Wyn Jones believes the Ospreys are hitting top form at just the right time with the race for play-offs heating up after their 41-10 bonus point victory over Treviso on Saturday.
"It's probably the best time of the season to start getting them," Jones told ospreysrugby.com.
"It's so tight up the top there. We were aware that there were a few teams ahead of us on 55 or 56 points, so the bonus point puts us just a little bit ahead of them so it's good that we're going in the right direction at this time of the season."
Dan Biggar was the inspiration for the Ospreys as they followed up their remarkable 23-22 win at PRO12 leaders Leinster, racking up 16 points with five conversions and two penalties and helping to set up tries for Ashley Beck and Paul James.
Ludovico Nitoglia did go over for Treviso in the 55th minute but tries from Joe Bearman and Tom Isaacs put the finishing touches on a commanding display from the Ospreys that leaves them in second place.
On Friday Ulster recorded a 45-7 win over Aironi at Ravenhill while Newport Gwent Dragons went down 27-19 at home to Connacht.
Edinburgh edged out Scarlets in an impressive 26-23 win as Glasgow Warriors trounced the Cardiff Blues 31-3.