The Ireland number 10, who will face off against Biggar in the Six Nations opener in four weeks’ time, kicked seven points and had a key hand in tries for Dave Kearney and Noel Reid, the winger adding a second late on.
Wales star Biggar kicked all of the home side’s nine points, but missed two kickable penalties which proved crucial in the final analysis as the visitors made it seven wins in a row and ended the home team’s winning sequence at five.
The Ospreys had decided to give the likes of Alun Wyn Jones and Justin Tipuric a break with key European fixtures looming, while Leo Cullen went with a strong side knowing his men have no chance of advancing in the Champions Cup.
Leinster started well, making the most of a poor Biggar clearance to pile the pressure on to their hosts.
Sexton and Ben Te’o made good initial thrusts but the Ospreys defence managed to keep its shape and rack up 22 tackles.
The Welsh side’s first foray forward proved a costly one for Leinster and Jamie Heaslip. The Ireland number eight appeared to be knocked out as he clashed heads with Te’o in attempted to halt rampaging Ospreys wing Jeff Hassler.
Heaslip attempted to get back to his feet but was soon back on the deck after a couple of unsteady steps before being helped off to give Ireland coach Joe Schmidt an unwanted headache just four weeks out from the start of the Six Nations.
His replacement, Dominic Ryan, was soon putting in plenty of tackles as the hosts spurned a kickable penalty in search of an opening try, with the pick and drive game working them up to the line, only for Richardt Strauss to make a punishing tackle and dislodge the ball from opposite number Scott Baldwin.
Biggar did knock over a well-taken drop goal to give them the lead, but Sexton soon began to take charge of proceedings as the Leinster pack got on top. Two punishing punts won the territorial battle and then two cross-kicks skewered the Ospreys defence, leading to the opening try.
The hosts had a warning when Sexton’s accurate boot found Isa Nacewa and forced them into defensive scramble mode, but they did not take heed and were punished when a pinpoint kick to the opposite wing ended with Kearney beating Sam Davies and Hassler to dot down.
Sexton added the extras and was at the heart of the action, winning a penalty after a late hit from Sam Underhill, before making an important strip on centre Owen Watkin.
Biggar settled the Ospreys after a difficult period with his second penalty but Sexton replied with a three-pointer as his clever kick isolated Brendon Leonard and allowed Sean O’Brien to force the penalty.
Biggar missed penalties either side of the interval, before making amends from close range when O’Brien was adjudged to have stolen the ball illegally.
The Ireland openside was frustrated again a few minutes later when he failed to gather a dropped ball from Ospreys full-back Dan Evans with the line after his mercy.
However, Leinster did not have to wait long to celebrate their second try. Sexton spotted an overlap and shifted the ball wide through Reid to Te’o. The Worcester bound centre committed two Ospreys defenders and offloaded back to the replacement who raced over in the corner.
Sexton struck the post with the conversion to keep the Ospreys within range, but Kearney finished the job as he slid over.
Penalties – Biggar 2, Drop Goal - Biggar.
D Evans (S Davies 18-30); J Hassler (E Walker 32), J Spratt, O Watkin (S Davies 68), H Dirksen; D Biggar, B Leonard (T Habberfield 70); P James (N Smith 59), S Baldwin, A Jarvis (M Fia 63), L Ashley, R Thornton (AW Jones 56), J King, S Underhill (J Tipuric 63), D Baker.
Tries – D Kearney 2, N Reid; Conversions – J Sexton 2; Penalty - Sexton.
R Kearney; I Nacewa, B Te’o, L Fitzgerald (N Reid 63), D Kearney; J Sexton (I Madigan 76), L McGrath (E Reddan 62); J McGrath (P Dooley 69), R Strauss (S Cronin 56), T Furlong (M Moore 56), D Toner, M McCarthy (T Denton 71), R Ruddock, S O’Brien, J Heaslip (D Ryan 7).
David Wilkinson (IRFU)
Edinburgh 28, Treviso 13