After Llanelli shocked their pool rivals and beat Moseley 40-17 at Parc y Scarlets to progress to the latter stages, Llandovery need just one point to join the west Wales side in the last eight.
With the Drovers five points clear of Saturday's opposition in second place, Lewis' men are favourites to progress and must play with confidence according to club captain Lloyd Phillips.
"It might be unlikely but at the end of the day Nottingham can still qualify so we can't play safe," he said.
"We need to start fast, get a lead and hopefully hang on."
The Drovers' brilliant league form has dropped a little since Christmas but the carrot of a place in the quarter finals is huge and they know a win would secure a home tie.
Phillips, who will miss the game with a dislocated shoulder suffered in an earlier round of the cup added: "Recent results haven't been as we would have wanted but Sunday is a massive game for the whole club.
"We struggled at times earlier in the season but we now have players who can come in and add strength in depth. A number of players have taken their chance, Adam Warren is an example of that and now he's in the Wales Under 20 side. Along with Warren, scrum half Rhodri Williams is also on Wales Under 20 duty this weekend.
"But I'm confident the team can get a win on Sunday - we just need to go out there and play with confidence."
There was a significant boost to Llandovery's hopes this week when centre Matthew Jacobs won the Principality Premiership Player of the Month award for January and he starts at outside centre with James Garland and Lee Rees at half back.
In the other British & Irish Cup games to take place, Cardiff face near rivals Bristol tonight with the English Championship side favourites to progress to the quarter finals from Pool 1 while Aberavon, who have been in improved form of late, travel to Rotherham.
Meanwhile in the Premiership, there are four games taking place this weekend with the highlight being a Gwent derby clash between Bedwas and Cross Keys.
Both sides go into the game on the back of disappointing results in the SWALEC Cup and will be looking to bounce back at the Bridge Field.
Bedwas make a number of changes from their cup defeat to Carmarthen Quins. Stuart Thomas starts at full back with Ethan Davies with the Wales Under 20 squad. Matthew Pewtner starts on the left wing in place of Mathew John while Simon Grainger returns to the back row to lead the side.
James Thomas starts in the second row in place of Phil Rees who drops to the bench with Ian George at loose head prop.
The two sides are separated by just four points with both hoping to keep up the pressure on league leaders Pontypridd. Bedwas secured a narrow 31-28 win when the two sides met earlier this season but with Keys welcoming back Rhys Peebles and Phil Williams from injury, they will be hoping to avenge that defeat.
At Sardis Road, Newport will be hoping to secure an unlikely league double with a win over Pontypridd. The Black and Ambers shocked the league leaders at Rodney Parade earlier this season but will be without Scott Sneddon who is out with a fractured arm. Tom Hancock starts at fly half and is partnered by Rhys Downes who will be facing his former club.
The home side continue to mix and match in their selection policy with Wales Sevens returnee Adam Thomas slotting in at full back, Dai Flanagan at fly half and youngsters Owen Jenkins and Joel Raikes both making a comeback from injury.
A new front row of Stuart Williams, Darran Harris and Chris Phillips will be utilised with veteran flanker Wayne O'Connor stepping into the back row.
In the other two games to take place, Swansea visit Carmarthen Quins as they look to move off the bottom of the table while on Saturday, Bridgend host Neath at the Brewery Field in an early kick off (11.30am).
Last weekend the two clubs experienced contrasting fortunes in the SWALEC Cup, Neath knocking out holders Cross Keys while Bridgend lost to championship side Bargoed.
Neath coach Patrick Horgan said: "I thought we were magnificent last week and the game had everything - it was fast, all-action stuff but we all realise that there can be no resting on our laurels. Bridgend is always a big challenge, all the more so after their defeat last week which will have disappointed them.
"We must push onwards and keep improving. Earlier in the season, Bridgend messed around with our scrum and stifled us at the contact area so we will need to counter that if we are to play with the style we want to."
Bedwas vs Cross Keys (Friday KO 7.15pm)
Swansea vs Carmarthen Quins (Friday KO 7.15pm)
Pontypridd vs Newport (Friday KO 7.15pm)
Bridgend vs Neath (Saturday KO 11.30am)
British & Irish Cup:
Bristol vs Cardiff (Friday KO 7.55pm)
Rotherham vs Aberavon (Saturday KO 2.30pm)
Nottingham vs Llandovery (Sunday KO 2.15pm)