Irish were already trailing 10-0 by the time of Shingler's indiscretion but they fought back to win the final hour 18-14 and could even have snatched a dramatic victory thanks to a spell of sustained pressure right at the death.
"I thought the effort was outstanding. To play 59 minutes with 14 men and give yourselves a chance to win the game is an absolutely incredible effort," said Booth.
"That was brought about by playing quite cleverly, an enormous forward effort and an outstanding scrum performance. It also indicated the level of fitness of our players because they were certainly finishing the stronger against 15 men.
"I was delighted with the ambition as well. With two minutes left on the clock and six points down, we were potentially risking a losing bonus point but, after last week, we wanted to put our best foot forward and I was encouraged by our attitude.
"We got ourselves into their 22 with lots of ball and it would have been an interesting situation if we'd have been three points or less down. We were on the receiving end last week against Edinburgh when we didn't slot a last-ditch penalty but they're the margins in the Heineken Cup and we need to learn those quickly.
"There's plenty of positives to take but we have to look at how we got ourselves into that position. I'm delighted with how they responded to adversity but the key to success is not getting into adversity in the first place."
As for the sending off, Booth had no complaints given the precedent set by Sam Warburton's dismissal when Wales played France in the World Cup semi-final.
Booth stressed that there was no malice from former Scarlet Shingler but he could understand referee Jerome Garce's decision.
"The way the game is being officiated and looked at around the tackle in particular means that, if you're not 100 per cent precise and in control of your emotions, you might pay a price," added Booth.
"To be fair to the lad, he was absolutely devastated. He's a young man coming back to Wales who wanted to impress. The guy's jumped up, he's followed through and the red card is the unfortunate outcome.
"This is a contact sport and players' decisions can change in one hundredth of a second. The physical ability - and I'm taking about agility as well as strength and power - means that sometimes they're going to get those decisions wrong.
"From a tackle technique point of view - low, grab tackle, drive through the point of contact - it was good technique, but you can't take people across the horizontal. That whole tackle lasts maybe two tenths of a second but these are the margins you have to deal with.
"The safety of the players is always paramount and we have to look after that. The game is changing and every team and all the players have to adapt to that pretty quickly."
Defeat to Edinburgh in Round 1 has left Irish behind the eight ball in Pool 2 and Booth admits that reaching a second quarter-final in six seasons in the Heineken Cup is now a huge ask.
But with unbeaten Edinburgh and the Blues due to play each other back-to-back next month, Irish could be right back in the mix if they can beat Racing Metro home and away.
"We need to win our next four games without question. Taking on Racing Metro home and away is going to be very, very difficult with the resources they've got. But it will be another experience that we'll hopefully be better prepared for, plus we'll have players back which is good.
"Then we've got to hope the Blues and Edinburgh take points off each other. At least then we'd have a chance to control our own destiny.
"Things are partly out of own hands now but the competitive spirit can take you a long way - we've seen that in the game against the Blues."