With Barca hosting Manchester United in the second leg of their Champions League semi-final on Tuesday, Valverde rested the likes of Lionel Messi and Sergio Busquets, while Luis Suarez and Gerard Pique were both suspended for the trip to Aragon.
It was a first top-flight win over Juventus for Spal which has gone through bankruptcy and been refounded twice - in 2005 and 2012.
It means United will have to go to the Nou Camp and get a result with the odds stacked against them - but they were at the Parc des Princes before the Red Devils mounted a 3-1 comeback over Paris St-Germain.
"If we had put all our regulars in it would have been easier to win it, but there is also the goal to obtain on Tuesday".
Cristiano Ronaldo became the first man to reach 125 goals in the UEFA Champions League when he scored against Ajax in mid week, but his goal record in the competition from the QF stage tells a story of its own.
The Brazilian global was a really busy player in the middle of the pitch, completing 64 passes at a successful rate of 86.5%, winning five of the attempted nine duels and dribbling past two players whilst in possession of the ball.
"If you don't believe that, then you just let them go through".
Allegri experimented with an eye towards the quarter-final, second leg game against Ajax after a 1-1 draw in Amsterdam.
Messi has 44 goals for Barcelona this season, and has been playing as well as he ever has in the run-up to this tie, but he had an off-night as he was shackled by Manchester United's midfielders.
"A lot of things happened because we played with a new system, with three at the back". They've earned four more victories under Francisco, which have seen Huesca's per-match return rise to 0.826.
With the game at 1-1, there was also a Juventus debut for England U20 striker Stephy Mavididi.
But SPAL held on to move up to 13th, seven points above the drop zone, having already beaten Champions League-chasing Lazio and Roma.
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