Jonathan Sexton was in man-of-the-match form for Leinster as he steered the European champions to their fifth win on the trot against the Ospreys.

Sexton thumped five penalty goals through the Liberty Stadium posts, with a final quarter drop goal from Isa Nacewa adding some cushion to the visitors' lead.

All Black back rower Jerry Collins was driven over in a maul for his second try in three games for the Ospreys, but James Hook could only add two penalties with the boot.

The Ospreys' indiscipline up front ultimately cost them. Late in the first half, they lost Collins and prop Duncan Jones to the sin-bin.

The hosts stood up well while down to 13 men, only conceding a penalty from Sexton, and though Hook was able to kick the Ospreys into an 11-9 lead - a strong finish saw Nacewa and Sexton kick Leinster home.

In his 100th game for the region, centre Andrew Bishop led the Ospreys and Lions duo Lee Byrne and Tommy Bowe made their first starts of the season.

There were three more Lions tourists on the home bench, including Shane Williams who replaced Gareth Owen in a late change.

Leinster had the experienced Eoin Reddan and Nathan Hines making their full debuts, Gordon D'Arcy came in for his first start of the campaign and recent debutant David Kearney, younger brother of Rob Kearney, retained the number 11 jersey.

Michael Cheika's men took the lead in the fourth minute, Sexton planting his first penalty over after Marty Holah was pinged for not releasing at a ruck.

Hook levelled three minutes later, though Leinster seemed to have the better of the opening exchanges. Sexton and Nacewa kicked intelligently, bringing their side up to the Ospreys 22.

Byrne saw plenty of possession early on as he swept up at the rear but his own kicking radar was slightly off and there was little to excite the home support.

A forceful burst from big winger Nikki Walker raised hopes of a long range counter attack and Jamie Nutbrown was close to putting Bowe over in the right corner, his pass being just slightly astray.

Leinster enjoyed a decent spell close to the home posts after the Ospreys had failed to deal with a garryowen. Additional pressure came in the scrum, however the Ospreys secured a relieving penalty and their line remained intact.

Sexton kicked his second penalty on the 15-minute mark, after referee Peter Allan spotted some crossing between the Ospreys backs.

Hook was off target with his next attempt, awarded for a ruck offence by Shaun Berne. Nonetheless, Collins' try followed in the intervening minutes.

The Ospreys pack powered forward off a close range lineout maul and Collins was shunted over as Leinster dropped their defensive guard.

That proved to be the first score of a nip-and-tuck first half. The Ospreys did very well to hold onto their 8-6 advantage for the break, following two penalty misses by Sexton and a number of scrums close to the home whitewash.

Leinster should have mustered a try - Sexton missed a gilt-edged chance to send the supporting Shane Jennings over - and then the yellow cards came.

First Collins was binned for raising his fists to Sean O'Brien in retaliation, and then loosehead Jones quickly followed him to the sideline for failing to keep his bind up in the scrum.

Incredibly, the Ospreys' weakened scrum, which included Bowe on the blindside, secured a penalty for a binding offence just when Leinster looked set to make their numerical advantage count.

The sides began the second half with a penalty apiece from Sexton and Hook, and the Ospreys, restored to their full complement, sent for reinforcements in the form of Williams, Mike Phillips and Alun Wyn Jones.

But the Lions trio had little say in the end result. Williams erred in possession, allowing Leinster to build again and Nacewa drilled his drop goal over for Leinster to retake the lead.

Just before that, replacement Fergus McFadden was denied a try by a terrific cover tackle from Hook.

The Ospreys grew more desperate as the minutes went by and their frustrated forwards gave away two more penalties, which Sexton coolly knocked over to stretch his side's lead to seven points.

The home side pressed on for a late try but it never came and stand-in captain Holah's poor attempt at a cross-field kick just about summed up the Ospreys' night.

Speaking afterwards, Sexton said: "It was a really tough game, we were probably defending for the majority of it.

"They've got some really big ball carriers and went through the phases, but we'd prepared all week for that.

"We manned up in the second half when we were up against it.

"It's tough to come to Wales and get a result. It's early season for the Ospreys, they've got a lot of players coming back and I'm sure they've got a strong side who will go well for the rest of the season."

Ospreys director of coaching Scott Johnson summed up in the mood in the home dressing room as the Welsh region came to terms with their second successive home defeat.

"This week I think I'm more disappointed than last week, as much as last week really hurt us," he said.

"I thought the effort was fantastic, it was 'A' for effort. In execution, and option taking, you have to go to the other end of the alphabet to find that one out. That was what disappointed us most.

"You look at that game, and as much as Leinster did, and as well as they did, they've come away with the scoreboard, but I think that we lost that game ourselves.

"It's great to have the endeavour to want to play the rugby, but some of the execution was disappointing. It's not through lack of effort, if it was I'd be despondent. I'm just disappointed that we let ourselves down."