The Heineken Cup champions were humbled 45-20 by the Welsh side last week although Madigan was in fine form then with 15 points.
And the 23-year-old again slotted superbly into Sexton's fly-half role for Leinster as they thrashed Newport Gwent Dragons 45-25 to put himself in the mind of the selectors for the upcoming RBS 6 Nations.
Welsh international Dan Evans popped up with a try for Dragons but they were outplayed by the Irish side who saw five different try scorers including hotly-tipped young winger Andrew Conway.
Ireland flanker Shane Jennings also got in on the action as Leinster ran wild and put their campaign firmly back on track after the first week stutter.
Ospreys winger Hanno Dirksen recently revealed he turned down a chance to play for the USA in the 2011 World Cup to push for a place in the Wales team and he did his chances no harm with a try against Ulster.
However it wasn't enough for the speedster, who will qualify for Wales in 2014, as reigning champions Ospreys continued their terrible start to the season with their second loss in as many games.
This time it was to Ulster but in a very close match and it took a converted try six minutes before the end from Ireland Wolfhounds scrum-half Paul Marshall to take the visiting side out on top 16-13.