Mick O'Driscoll, Howlett and James Coughlan added further tries and Ronan O'Gara kicked a total of 15 points.
He produced a superb run around in midfield with Brian O'Driscoll before Gordon D'Arcy freed Horgan.
Ireland coach Declan Kidney said it was difficult to assess O'Driscoll's contribution to Irish rugby.
"I am surprised that Paul O'Connell got the captaincy ahead of Brian O'Driscoll, " he said.
Centres Brian O'Driscoll (concussion) and Jamie Roberts (wrist) were also ruled out of the third Test.
But member Debbie Driscoll said two planned walkways would be dangerous, due to traffic.
Fly-half Robinson failed to convert and after Mick O'Driscoll fell offside, fluffed another kickable penalty attempt.
Wallace will partner captain Brian O'Driscoll at centre with Trimble named at left wing.
Captain Brian O'Driscoll will earn his 100th Ireland cap in Saturday's match at Croke Park.
Doncaster boss Sean O'Driscoll claimed he saw Rangel taking aim for Wellens during the same incident.
Driscoll predicted that Dent would be a rubber stamp for the national GOP if elected.
Driscoll further faulted Dent for voting against the Rendell administration's income-tax plan in 2003.
"Before the round I was glued to the TV and the news, " Driscoll said.
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For his winning suggestion, reader Joe Driscoll gets a shout out and bragging rights.
Roberts's centre partnership with Brian O'Driscoll has been one of the most effective combinations on tour.
Brian O'Driscoll and Rob Kearney produced superb breaks but poor handling prevented any Leinster tries.
But an O'Driscoll break in the 14th minute yielded a penalty and Contepomi slotted the kick.
That try moved O'Driscoll clear of team-mate Denis Hickie as Ireland's all-time leading try-scorer, with 30.
O'Driscoll played in all three Lions Tests on their unsuccessful 2001 tour to Australia.
"I thought Anthony Allen, in particular, looks a great prospect, " said O'Driscoll after Leinster's 37-20 win.
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Ireland captain Brian O'Driscoll also attempted to take the positives from his team's victory.
Brian O'Driscoll, Earls, Rob Kearney and Shane Horgan added further touchdowns after the interval.
But then CEO Brian Driscoll abruptly quit and relations between union and management deteriorated further.
Two O'Gara penalties nudged Munster 9-6 ahead but Sean O'Brien set up O'Driscoll's decisive 70th-minute try.
Ireland had led 13-9 at half-time thanks to Brian O'Driscoll's record-equalling 24th championship try.
Indeed, the Irish side were also the more fluid, despite being without the injured Brian O'Driscoll.
Mick O'Driscoll returns to the Munster squad after missing Sunday's defeat in Cardiff with an ankle injury.
Consider this discussion as reported by the New York Times with experts Jay Fahy and Michael Driscoll.
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Despite O'Driscoll leading Ireland to the Grand Slam, his team-mate Paul O'Connell appears to be the favourite.
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