But Irish came roaring back as Matt Garvey crossed twice, with George Skivington and Shane Geraghty also on the scoresheet as they gained a measure of revenge for their defeat at the Salford City Stadium last weekend in the Aviva Premiership.
But Charlie Amesbury's late try for Sale did send them home with the consolation of a losing bonus point, much to the disappointment of Smith.
"We made it hard for ourselves in the first half, but we did what we had to do in the second half and got a result," he said.
"Denying them a losing bonus point is irrelevant because they are not in our pool, but you want to be ruthless.
"We came with a lot of attacking intent, but I am not happy with the defensive intensity.
"That was the story of our afternoon defensively. All three of their tries were soft.
"We showed in the first half that we wanted to be positive, and we had a couple of opportunities in their 22, but they wriggled off the hook. We had to be patient.
"The try Sale scored prior to half-time was unacceptable. I was coming down the internal stairs and did not not see it until after the game on the highlights.
"But we were pretty annoyed and had a simple plan in the second half.
"We felt our forwards were starting to get on top so we let the pack loose on them and we were a bit more precise in the second half.
"The good thing is that it ended well thanks to Shane's intercept try which got us the bonus-point win.
"Garvs (Matt Garvey) is in really good form and it was great to get George (Skivington) out on the park.
"He showed a fair bit of hunger, while Bryn Evans has played almost every minute of every game. It's a good combination which worked well.
"This sets us up well in this competition. Next Sunday we go up and have a crack at Leicester."
Meanwhile Sharks CEO Steve Diamond was left to reflect on what might have been as his side led 21-10 early in the second half before heading home with only a losing bonus point.
"We should have won," he said. "Some of our players showed naivety by losing control. We gave nineteen soft points away. We'll lick our wounds and look to come back strong on Friday."
London Irish: Watson; Ojo, Tagicakibau, Geraghty, Gaston; Humphreys (Shingler, 77), Allinson; Corbisiero (Yanuyanutawa, 61), Blaney (Ellis, 72), Halavatau (Griffiths, 72), Skivington (Low, 77), Evans, Garvey, Gibson, Hala'ufia (Gray, 50)
Not used: Peters, Murphy
Sale Sharks: Miller; Amesbury, Addison, Jennings, Shepherd; Cipriani (Uys, 73) , Peel (Cliff, 72); Harrison, Taylor (Cruse, 71), Cobilas (Buckley, 56), McKenzie, Gaskell, Powell (Myall, 30), Vernon, Easter
Not used: Flynn, Bordill, Davies
Tries: Garvey 2, Skivington, Geraghty
Conversions: Humphreys 4
Penalties: Humphreys 2
Tries: Peel, Cipriani, Amesbury
Conversions: Cipriani, Miller
Penalties: Cipriani 3
Referee: Ian Tempest