The black, green and gold were 26-7 down at half-time after being hit by four Irish tries, but Saints roared back in the second period to level at 26-26 with eight minutes to go.
It wasn't to be the home side's day though as they conceded a score to Benhard van Rensburg just moments after he had returned from the sin bin.
And Rory Jennings kicked the conversion and a penalty to make sure of the Irish success in the Premiership Rugby Cup opener at cinch Stadium at Franklin's Gardens.
Dowson said: "Taking into consideration the number of people who played for the first time, making their debuts, and the age profile of the group, we showed tremendous character and resolve to come back to level in the final 10 minutes.
"To concede late on was frustrating because we got all the way back in the game and then we kind of butchered it.
"There were some good parts, some bad parts and there was so much to learn for a young group.
"We showed composure and character - two things we want to see when we identify our players.
"We got caught a little bit cold at the start and London Irish came out and put us on the back foot.
"We were a bit slow to get into the game and we gave them a head-start, but fair play to the guys for coming back in the second half.
"We were very dominant in that second half for long periods, apart from the last five minutes."
There were some moments to remember for Saints' young guns, notably a debut score from full-back George Hendy.
"All of the debutants did well," Dowson said. "I was really pleased with people like Tom Lockett and Geordie Irvine, even though he only had a 10-minute cameo.
"Ollie Newman did well coming back from injury so there were lots of guys there putting their hand up.
"The guys who had played before hadn't played a lot of rugby - players like Josh Gillespie, so it was great to see him out there getting that experience and playing well.
"Jimmy (Grayson) has been working hard at his game, Hutch (Rory Hutchinson) got some game time, Reece Marshall was back in the fold.
"It was good for lads who have been at Bedford to come back, put a Saints shirt on, play in front of a decent crowd at a good level of rugby and that's what we want.
"That's what this tournament is about."