Smith scored a try in each half as Tigers took what appeared to be an unassailable 31-16 lead into the final six minutes.
However, Irish threatened a remarkable comeback when they scored two tries in the space of three minutes to cut the gap to just three points.
Smith, who had been substituted on 58 minutes after receiving a first-half knock, said he found himself in the tunnel for the dying moments because it was too nerve-wracking to watch from the dugout.
The Tigers Academy graduate said: “I got a knock in the first half and eventually had came to off. It was disappointing because it is hard when you see the guys at the end and they are putting their bodies on the line. It was a shame I couldn’t be out there.
“The nerves were going. I was in the tunnel. I couldn’t watch it in the dugout because I was getting too nervous – but we held on.”
Smith’s two tries took him up to six for the season. He admitted to a few nervous moments when his first effort was referred to the television match official and paid tribute to his teammates for his brilliant second score.
“I thought Julien (Dupuy) was going to miss me out on the first one,” said the Tigers centre. “He hit me, someone tried to tackle me but slipped off. Johne (Murphy) was telling me that if I didn’t score he was going to have a word because he was open.
“There was a nervous moment but luckily I wasn’t held so it was good to score.
“The second one was a great backs move. I think most of the backs touched the ball and I was the lucky one to get on the end.
“Alesana (Tuilagi) is playing really well at the moment and that try was more for him and his pass.
"It was a whole team performance. It was good."
Tigers return to Welford Road on Saturday for a Guinness Premiership game against league leaders Gloucester. A limited number of tickets remain on sale through the ticket office on 08701 28 34 30.
