Deacon, who was also named man of the match in their winner-takes-all encounter with the four-time European champions, inspired the Tigers to a gritty 9-5 victory at a snow-covered Welford Road.
Three Toby Flood penalties proved decisive for the hosts while both Lionel Beauxis and Luke McAlister combined to miss five kicks at goal for the French powerhouses.
Yoann Huget crossed for the only try of the match but that was not enough as the Aviva Premiership side held out frantically at the end to progress at the expense of their French opponents.
And Deacon, who along with Geoff Parling provided a real nuisance at the lineout all match long, paid tribute to the passion his side had shown to progress.
"We really had to grit our teeth and dig deep at the end," said Deacon, whose Tigers side will now travel to Toulon in their quarter-final.
"We were holding out at the end but we knew how much we needed the win and we do not lose many games at home.
"I think that we wanted it more in the end but it was not easy and we really had to fight hard but to be honest I quite enjoyed those conditions."
Elsewhere on Sunday, Saracens secured a home quarter-final against Ulster as they secured a bonus-point win against Edinburgh at Vicarage Road.
Chris Ashton crossed twice in their 40-7 win against Edinburgh and earned the praise of his head coach Mark McCall.
"It was great to see Ashy [Chris Ashton] score a couple of tries and getting back to what he really does best," he said.
"The second try was fantastic and I wish I could claim credit for thinking that up - Ashy and Owen [Farrell] just saw each other and they pulled it off.
"We can appreciate just how difficult it was out there and we said after the game that the conditions were as bad as it gets with the ball like a bar of soap."
On Saturday Jim Mallinder was forced to concede that Northampton Saints deserved to go out of the Heineken Cup after a late Peter Horne try condemned them to defeat against the Glasgow Warriors.
Mallinder's side, currently fifth in the Aviva Premiership table, came into their final clash of the Pool stages knowing that a bonus-point victory could keep their slim qualification hopes alive.
But it was not to be as, despite running in three tries through Dom Waldouck, George Pisi and Ben Foden they fell to a 27-20 defeat.
And Mallinder admitted afterwards that his side's inconsistency had been the downfall of their European campaign.
"We showed that when we want to we can get performances; the win at Ulster away - the only visiting team to win at Ravenhill this season - was magnificent for us," he said.
"But to win these competitions you need to be more consistent.
"We won three games and lost three games and that isn't good enough.
"We came up here to try and get to the quarter-finals of the Heineken Cup. We knew it was an outside chance, we needed four tries. We were close, but we weren't close enough."
Elsewhere in the Heineken Cup on Saturday Sale Sharks' disappointing campaign finished off with a 26-14 at Cardiff Blues.
A much changed Sharks side ran in two scores through Tommy Taylor and Aston Croall but were overpowered by the Welsh outfit.
Tries from Lloyd Williams and Michael Paterson in addition to 16 points from the boot of Leigh Halfpenny proved the difference as Blues won their first game of their European campaign.
And Exeter Chiefs made a good fist of welcoming reigning champions Leinster to Sandy Park but ended up 20-29 losers.
With the Irish region desperate for a bonus-point win that could keep their qualification through to the knock-out stages alive they had run in four tries by the 53rd minute.
The Chiefs scored two converted tries of their own with a penalty score and a Neil Clark effort in addition to two penalties from Gareth Steenson.
And on Friday Harlequins secured their sixth straight win in the competition with a 16-9 win over Biarritz.
Tom Guest crossed for the game's only try while the boot of Nick Evans did the rest as they secured a home quarter-final against Munster.
SCORERS:
SUNDAY:
Saracens 40 Edinburgh 7
Saracens
Tries: Ashton 2, Stevens, Hodgson, Wyles
Penalties: Farrell 3
Conversions: Farrell 3
Edinburgh
Tries: Tonks
Conversions: Laidlaw
Leicester Tigers 9 Toulouse 5
Leicester
Penalties: Flood 3
Toulouse
Tries: Huget
SATURDAY:
Glasgow Warriors 27 Northampton Saints 20
Glasgow
Tries: Strauss, Matawalu, Horne
Conversions: Wight 2, Horne
Penalties: Jackson 2
Northampton
Tries: Waldouck, Pisi, Foden
Conversions: Myler
Penalties: Myler
Cardiff Blues 26 Sale Sharks 14
Blues
Tries: L Williams, Paterson
Conversions: Halfpenny 2
Penalties: Halfpenny 4
Sale
Tries: Taylor, Croall
Conversions: Miller 2
Exeter Chiefs 20 Leinster 29
Exeter
Tries: Clark, Penalty
Conversions: Steenson 2
Penalties: Steenson 2
Leinster
Tries: D'Arcy, Kearney, O'Driscoll, Heaslip
Conversions: Sexton 3
Penalties: Sexton
FRIDAY:
Biarritz 9 Harlequins 16
Biarritz
Penalties: Yachvili 3
Harlequins
Tries: Guest
Conversions: Evans
Penalties: Evans 3
