More than 36,000 people attended the Millennium Stadium where the Newport Gwent Dragons took on the Scarlets and Cardiff Blues met the Ospreys.
Coombs' side may not have been winners on the day, George North scored twice to give the Scarlets a 20-28 win, but the likes of Jonathan and Dan Evans impressed as they both went over for a try apiece.
And Coombs reckons their performances could have nudged the Welsh selectors.
"Today was fantastic, you can't ask for anymore at regional level," Coombs said of the Judgement Day experience.
"A lot of boys won't often get the chance to play on that field but after today, there might be some who will.
"Dan Evans showed what he could do at 10 in an unfamiliar position and he put in a big performance. Hopefully the Welsh selectors will be looking at him."
Coombs led the Dragons for the first time on Saturday and alongside Toby Faletau, combined to negate the Scarlets' power. Faletau in particular had a monumental impact, his work in the loose particularly impressive.
But although the Dragons refused to give a yard, it was the Scarlets who emerged with a win that keeps them in contention with the Ospreys for a play-off spot.
"Obviously we came here to win. It didn't happen but we had a five minute period in the second half where we just switched off and the Scarlets scored two tries," Coombs added.
"We fought hard throughout the game and we showed some great character to get back into it in the second half.
"We're an honest bunch and we haven't been where we've needed to be in the last few weeks. Today was about putting us back on the map and giving the crowd what they deserve.
"I think we gave them something to cheer about, it was some of the best rugby we've played. We had an attitude to give it 100 per cent and that's what we did."
Another Dragon who impressed on Saturday was Dan Lydiate who continued his return from injury by playing an hour at the home of Welsh rugby.
And Coombs revealed his side were motivated to produce a performance for the Welsh flanker.
"Dan Lydiate is not with us next season so there was a big statement in the changing rooms that we wanted to give something back to Dan," he said.
"He's had so many injuries playing in the Dragons shirt and we delivered a performance. Now it's about getting a win."