Gatland was in attendance at Parc y Scarlets as big-money tighthead prop Thomas, on a reported £180,000 a year, scored two first-half tries in the nine-try rout over Connacht.
Jonathan Davies and Regan King also added doubles for the hosts while Josh Turnbull, Rob McCusker and Sean Lamont crossed to beat their previous best of 53-11 against the Borders in 2007.
And Scarlets coach Nigel Davies believes Thomas could make a late surge into the national set-up ahead of summer Tests with South Africa and the tour to New Zealand.
Davies said: “Rhys has not had the greatest start to his Scarlets career and has had a lot of injuries. But he showed what he is capable of today.
“He’s a very good ball player with the ball in hand. He has put himself in contention for Wales and done his chances no harm.”
