It was their fourth win on the trot with a maximum 20-point return from those games.
But Thomas' path to the No10 jersey has been blocked by former Scotland fly-half Gordon Ross, who has been in fine form for the Old Deer Park outfit. That has confined Thomas to just one start in the Championship club's nine games this season.
But Thomas grabbed his opportunity with both hands with a match-winning performance after Ross hobbled off mid-way through the first half.
"It's been tough and frustrating; it's been a bit of a patience game," said Thomas.
"But it was good to get some pitch time and thankfully it went well.
"Gordon's been playing really well at 10 and Errie's [Claassens] been playing really well at full back, so it's all about waiting for your chance and if you get an opportunity you have to try and take it.
"When you're on the bench you've just got to prepare as if you were starting and try and keep switched on at all times as you never know what can happen."
Thomas, who is in his third season at London Welsh, grabbed two opportunist tries in his virtuoso display.
"I saw there was no one behind and I called to Runci (Nick Runicman) to kick it over and he'd spotted it a well. He put a great kick in and luckily enough it bounced perfectly for me," added Thomas.
That first try helped the Exiles into an 18-9 half-time lead, but with the result in the balance, Thomas charged down Nick Little's attempted clearance and scampered over for his second try.
That opened the floodgates with Marland Yarde - on loan from London Irish - scoring with his first touch for Welsh and Liam Gibson claiming his sixth try of the season.
"Another lucky bounce; I just gambled on the charge down," added Thomas talking about his second score.
"You're always trying to get to the kicker and luckily enough I got the charge down and the ball bounced straight into my hands again. We never looked back from there, scoring two cracking tries after that.
"It was clinical performance against a good team - I don't think the league table does them justice because they're a tough physical side, so to get five tries against them is really good."
While biding his time, Thomas has benefited from the link-up with London Irish, playing in four Monday night A League matches for the Aviva Premiership club.
"It's been really good to help keep my match sharpness up, so when an opportunity does arrive you're in the best frame of mind to do as well as you possibly can," said Thomas, who played against Harlequins and Gloucester at full back and Bath and Saracens at fly-half.
Next up for the Exiles is a tough trip to Goldington Road to take on Bedford Blues, who are coached by former Cardiff and Wales full-back Mike Rayer.