Walter Mazzarri's Napoli - the joint Serie A leaders - took the liberty of resting a host of stars for Thursday's Europa League game at PSV Eindhoven, and the Italians were duly humbled 3-0.
Udinese have stumbled through their domestic campaign so far, and were not expected to get a positive result from their European outing at Anfield, but instead stunned Liverpool with a 3-2 victory.
Guidolin could barely hide his delight following the famous victory but warned his players to beware a wounded Napoli.
He told Gazzetta.it: "They've given me a wonderful gift, it was a magical evening that I will remember for the rest of my life.
"At the break I thought the players were looking a little down so I tried to cheer them up because there was still time to get a result.
"It's a victory that gives us momentum and a morale boost going to Naples, but the fact they lost is very dangerous.
"Often the team that wins relaxes and the team that loses fights back. But we'll give them a game.
"I'm happy with this extraordinary result. We're a different team than we were last year, we have to recognise that fact but keep believing in ourselves."
Talismanic striker Antonio Di Natale was among the goals on Merseyside and should start up front alongside Mathias Ranegie, while Maurizio Domizzi and Luis Muriel sit out.
Mazzarri paid the price for leaving star striker Edinson Cavani on the bench against PSV, and his introduction for the second half was not enough to salvage a result.
The Napoli boss admitted his decision to heavily rotate his squad might have been to blame for the defeat but his priority remains challenging Juventus for the Serie A title.
"This year our mission is to drop as few points as possible in the league, that is the decision of the club," he told Gazzetta.it. "But this defeat will certainly help us improve and grow."
Cavani should return alongside Goran Pandev, with Eduardo Vargas and Lorenzo Insigne returning to the bench. Captain Paolo Cannavaro is suspended, allowing Alessandro Gamberini to deputise.