Sexton arguably delivered his finest performance in a blue shirt since his return to the Irish province over the summer - setting up Dave Kearney's first try with a brilliant cross-field kick.
Dan Biggar, who did not enjoy his most accurate night off the tee, pulled Ospreys back to within one point in the second half but that is as close as the hosts came.
Shortly after, replacement Noel Reid scampered over for Leinster, and Kearney tied up the 22-9 victory with another powerful finish late on.
The win moved Leinster top of the GUINNESS PRO12 table and man-of-the-match Sexton admitted it took a performance of some note to down the Ospreys.
"We knew they were on a good run of form - they've really turned their form around and they have been pretty impressive in Europe as well," he said.
"We know they've got a big game next week and they left a few of their big guns on the bench but we did really well to cope with the conditions and with them.
"They're a quality side and a real close-knit squad as well.
"In the past sometimes we've taken our eye off the ball in the final PRO12 game before a European break because Europe has been so big for us but we're out of Europe now, so this was the big game for us over the next couple of weeks. We wanted to leave this competition on a high."
Ospreys had been on a five-game GUINNESS PRO12 winning streak and though Sexton concedes Leinster's performance wasn't perfect, it came close under the circumstances.
"The conditions were miserable and the ball was greasy even before kick-off. It was tough but thankfully we did all the right things," added the Ireland fly-half.
"We gave away a stupid couple of penalties towards the end which put us under pressure but we're delighted to get the win against a good side."
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Guinness PRO12 Leinster News
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