|Glasgow Warriors (6) 12|
|Pens: Clegg 4|
|Leinster (6) 6|
|Pens: Nacewa 2|
Glasgow Warriors leapfrogged rivals Edinburgh and climbed into the Pro12's top six with a hard-fought victory over profligate Leinster.
In a bruising affair played out on a badly damaged pitch, there was scant attacking precision on display.
Rory Clegg's quartet of penalties trumped two from Isa Nacewa.
Glasgow's dogged scrapping at the breakdown was pivotal, while Leinster maddeningly squandered much of their field position.
Visiting captain Nacewa knocked over a fourth-minute penalty to nudge the visitors ahead when Glasgow went off their feet at the breakdown.
Leinster rampaged downfield from the restart, hooker James Tracy shimmying his way into space through the Warriors' midfield. His backhand offload found Nacewa, but a fine cover tackle from James Eddie halted the move in the phases that followed.
Rory Hughes, the Glasgow winger, was withdrawn with a head knock in the 11th minute after a thunderous upright collision, Glenn Bryce his replacement.
Clegg, returning from an eventful spell in the Top 14, struck two penalties of his own as Glasgow edged in front with 20 minutes gone, amid roars of "Come on, George!" rasping down from the home coaches' bench bound for referee Clancy.
Leinster's bruisers were puncturing the hosts' midfield with concerning ease but the visitors butchered what can only be described as rugby's equivalent of an open goal.
Fly-half Cathal Marsh, inside the Glasgow 22, had no fewer than four men to hit with Bryce scrambling desperately to cover, but floated a huge miss-pass behind Nacewa and into touch.
Relief for the Warriors, exasperation for Leinster, who made do with three more points from the captain's boot rather than the five, or seven, they ought to have had.
Sila Puafisi, for a neck roll, then Simone Favaro, at the breakdown, were penalised for the hosts as the clock ticked red. Nacewa teed up for another shot at the posts from straight in front, but his strike flew wide, and the sides remained level at the break.
Glasgow centre Sam Johnson had already departed with another head knock, giving Nick Grigg a debut, and captain Peter Murchie became the third Warrior to depart when he failed to appear for the second half - prompting a reshuffle in the home ranks.
Scrum-half Ali Price replaced the skipper, with Grayson Hart moving to the wing and Bryce shifting back to full-back.
Glasgow nonetheless began the second period with more accuracy and dynamism. Clegg slotted his third penalty from inside Leinster's 22, then arrowed a fourth between the uprights when a Glasgow jumper was pulled down at the line-out.
With six minutes remaining, Grigg scythed down replacement scrum-half Isaac Boss around the neck, allowing for a late march towards the home line.
Again, though, the defending champions' breakdown nuisance saw them force a penalty - with a squad by that stage so stretched, and every point crucial in the race for a play-off berth, on such victories are seasons defined.
Glasgow Warriors: Murchie, Jones, Bennett, Johnson, Hughes, Clegg, Hart; Reid, Brown, Puafisi, Peterson, Nakarawa, Eddie, Favaro, Ashe.
Replacements: G. Bryce (for Hughes, 11), Grigg (for Johnson, 34), Price for Murchie (41), Holmes for Eddie (46), Cummings for Peterson (58), Fagerson for Puafisi (55), Malcolm for Favaro (62), Yanuyanutawa for Reid (62).
Leinster: Kirchner, Nacewa, Ringrose, Te'o, D. Kearney, Marsh, L. McGrath, Dooley, Tracy, Furlong, M. Kearney, Triggs, D. Ryan, Leavy, Murphy.
Replacements: Reid for Ringrose (76), Carbery for Marsh (76), Boss for L. McGrath (73), Loughman for Dooley (73), Bent for Furlong (73), Timmins for M. Kearney (64), Molony for Triggs (54). Not Used: B. Byrne.
Ref: George Clancy (IRFU).