boasting 100 per cent win records when they met in round five.
With the home side taking the spoils at Parc Y Scarlets and suffering just two defeats in their opening 12 it was they who topped the table at the half-way stage.
But six wins out of six, starting in round 13, saw Connacht rise up and lead the way before suffering defeat to Ulster which saw them dethroned by provincial rivals Leinster.
With three rounds to go, Leinster are the front runners after their win over Munster as they bid to secure a record-breaking fifth title.
Two home wins should be enough to secure them a play-off berth with Edinburgh, who they face on Friday, attempting to be the first Scottish team to win in Leinster since 2011.
Regardless of their result against Ulster in round 21, a bonus-point victory at home to Treviso, a side who have not won on the road all season, on the final day should be enough to secure Leinster a home semi-final.
Connacht, who trail Leinster on points difference, may have crashed out of Europe to a late drop-goal, but there was enough in defeat to suggest their league challenge won't fade.
Lam's men have an eight-point buffer to Saturday's opponents Munster, who sit fifth, and have won two of their last three fixtures against their interprovincial rivals.
Connacht will need to be on their guard against Benetton Treviso, who have won two of their last four at the Stadio Monigo, before taking on a resurgent Warriors at the Sportsground.
Glasgow have surged into the Guinness PRO12 play-offs having won all of their last seven games and they'll be looking to avenge their opening day defeat to Scarlets this weekend.
If they repeat last week's 43-14 victory over Zebre when the teams meet next week they could go into the final game against Connacht pushing for a home semi-final.
After disappointing Cardiff and Ospreys campaigns, Scarlets could be the only Welsh team in the play-offs. After back-to-back wins against Treviso and Ospreys, the Scarlets play-off push hit a bump against Cardiff Blues.
Scarlets face an in-form Glasgow side, who have made the past two finals, before they take on the Dragons in Judgement Day at Principality Stadium. Anything but a win will open the door for Munster, who Scarlets face in the final game of the season at Thomond Park.
Outside the top four, Ulster, Munster and Edinburgh are waiting in the wings ready to pounce.
Ulster's recent league double over Connacht demonstrated the potential in Les Kiss' side but they remain three points adrift of the top four.
And the Irish province, who have been play-off mainstays since 2013, follow a trip to Zebre by facing Leinster.
Munster face an uphill task if they are to make the play-offs for the sixth time in seven years. Though they are only one bonus-point win behind Connacht, all three of their remaining fixtures are against top seven teams. They have already lost to Connacht, who they face on Saturday, once this season.
Edinburgh arrive at Irish Independent Park the following week ahead of a final day battle against the Scarlets at Thomond Park.
Edinburgh's season will hinge on their next two trips to Ireland, against Leinster and Munster. Six points off the top four, at least one win will be required, at which point they'll have to beat Cardiff Blues at BT Murrayfield and hope other results go their way.
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