Munster edged ahead of Leinster on scoring difference courtesy of a 21-13 win over their Ulster counterparts at Abbeyfeale RFC.
The hosts were 8-3 to the good at half-time, with out-half Darragh Meade kicking a penalty and winger Barry Gibbons getting over for a try, after Ulster centre James Thompson had kicked a penalty.
Ulster, who beat Connacht last weekend, nipped ahead early in the second half when flanker John Hanna touched down and out-half Martin Irwin added the extras. Hanna and Irwin both play for recent Towns Cup winners Ballymoney.
But Munster had the better of the remaining half-hour, with Meade kicking two more penalties and converting a try from Newcaste West clubman Jerry Martin who was a dangerous runner with ball in hand.
Ulster's only response was a penalty from Irwin as they missed out on a losing bonus point.
Connacht lost out to Leinster in a competitive clash at Creggs RFC on Saturday, with a late try from centre Bevan Duffy proving crucial for the visitors in a 23-17 triumph.
Connacht looked impressive in the opening half and their clinical attacking led to two tries from centre Jordan Farrington and flanker Eoin Rooney, both converted by out-half Paddy Pearson.
Former St. Mary's College ace Barry Lynn accounted for Leinster's opening points - a drop goal and a penalty - as they turned around at the interval with a 14-6 deficit.
Coached by Declan O'Brien, Leinster leaked a penalty to Pearson as Connacht extended their lead, but the westerners had two players sin-binned in the closing stages of the second half - try scorer Rooney and replacement Mike Ward - and paid the price for their indiscipline.
Injuries to the impressive Farrington and Pearson also did not help their cause, and Leinster were call on replacements of the calibre of Seapoint's Stephen Verso and former Ireland underage international Brian Collins as the game wore on.
Connacht were overhauled when replacement Paul Devitt and the aforementioned Duffy crossed for tries which Lynn converted.
Duffy's score was a superb solo effort which saw him intercept Rooney's pass and dance his way over from 60 metres out.
The result extended Leinster's unbeaten run at this level to ten matches and they will have to overcome Ulster next Saturday in order to stand a chance of retaining the title.
2009/10 IRFU JUNIOR INTERPROVINCIAL CHAMPIONSHIP:
Saturday, April 24 -
Leinster 15 Munster 15, Seapoint RFC
Ulster 34 Connacht 23, Virginia RFC
Saturday, May 1 -
Connacht 17 Leinster 23, Creggs RFC
Munster 21 Ulster 13, Abbeyfeale RFC
Saturday, May 8 -
Ulster v Leinster, Coleraine RFC, 2.30pm
Munster v Connacht, Ballincollig RFC, 2.30pm
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