The Television Match Official ruled he had lost control in the act of touching down but a fired-up Munster pack turned over possession at the scrum and were awarded an attacking scrum of their own.
The home side finally gained dominance in the scrum and were awarded a penalty from the set piece on 55 minutes to make it 15-9.
That cost Worcester dearly, as from the next scrum, Quins were awarded a penalty try and Evans converted to complete the turnaround.
St Helens took the lead on seven minutes when they were awarded a scrum close to the line after Dimitri Pelo was bundled into touch from a Sean Long kick.
However, replays showed that the France scrum-half had recovered his hold of the ball a split-second before winger Thom, and referee George Clancy awarded a 5m scrum.
After Leeds squandered several promising attacks their set-piece scrum buckled and the visitors were awarded the first penalty of the game.
Ireland's scrum creaked late on as the Scots were awarded a penalty try but Johne Murphy scored a late Irish try.
But the visitors were awarded a penalty try from a scrum after 13 minutes and O'Gara converted, but Biggar struck back with two penalties.
Referee Nigel Owens awarded a penalty try after replacement Kings scrum-half Josh Fowles illegally came round to disrupt it on the Lions side, and O'Gara's conversion made it 20-3.
Steenson finally found his range in the 24th minute to open Exeter's account, expertly slotting over a penalty awarded after Northampton were penalised for collapsing the scrum.
When awarded yet another penalty, Harlequins elected for a scrum, not least because Hanks was missing and, one huge push later, Exeter caved in on their line, Davey awarding a penalty try which Evans converted.
Referee Nigel Owens awarded a penalty try but opted not to sin-bin Spice, ruling the scrum-half's infraction was only accidental.
Scotland were penalised at a scrum, Italy opted to pack down again and the second time the visitors offended, referee Nigel Owens awarded the penalty try.
When a fifth scrum was turned, Jacques Burger was adjudged to have dived on the ball in an offside position and Leicester were awarded a penalty try, converted by Twelvetrees.
Stephen Jones' kick-off epitomised the Scarlets' season thus far - off kilter as the ball ran dead, bringing a scrum on half-way at which the Wales fly-half must have been relieved to see a free kick awarded against Ulster.
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