Leicester: (10) 26
Tries: Varndell (2)
Cons: Humphreys (2)
Pens: Humphreys (4)
London Irish: (9) 18
Pens: Geraghty (6)
Tom Varndell's double helped a weakened Leicester to the points, with Ian Humphreys kicking the other 16 points.
Daryl Gibson and Dan Hipkiss set up Varndell's first try on two minutes with a length-of-the-field move.
Gibson should have made it two but he could not gather a Hipkiss pass so the half-time lead was 10-9, with Shane Geraghty scoring three Irish penalties.
Varndell's second try came just after the restart with Geraghty adding three more second-half penalties for Irish.
The result was all the more impressive as Humphreys was making only his third start for Leicester, while there were debuts for half-back partner Johnny Murphy and Gavin Hickie in the front row.
Leicester coach Pat Howard: "It was a massive step up for Humphreys, Murphy and Hickie.
"They are all third choice at the club and have shown a fair amount of character to show there's not a big gap between number one and number three.
"You have to have the right attitude and they saw there would be an opportunity at this time of year.
Howard added: "(Varndell's second) was an outstanding try and it was all his own doing. Tom's enthusiasm got that try."
London Irish director of rugby Brian Smith: "The first try came from very deep and we had to fight our way back and get into the game at half-time.
"It was very disappointing to concede another try so quickly after half-time."
Leicester: Vesty; Lloyd, Hipkiss, Gibson, Varndell; Humphreys, F Murphy; Moreno, Hickie, Holford, Cullen (capt), L Deacon, B Deacon, S Jennings, Crane.
Replacements: Buckland, Young, Hamilton, Abraham, Ellis, Cornwell, J Murphy.
London Irish: Horak; Ojo, Mapasua, Catt, D Armitage; Geraghty, Hodgson; Hatley, Russell, Lea'aetoa, Kennedy, Casey, McCullen, Magne, Murphy.
Replacements: Skuse, Coetzee, Hudson, S Armitage, Feaunati, Rees, Bishop.