Gasparotto, the winner of the 2012 edition, put in his decisive dig on the fourth and final ascent of the Cauberg in the closing moments of the 252-kilometre race in the southern Netherlands.
The 34 year-old reeled in Belgian escapee Tim Wellens (Lotto Soudal) before holding the streamlined peloton at bay with Valgren, who had managed to latch onto Gasparotto's attack on the punchy 1.8km climb.
With the peloton closing in on the home straight, Gasparotto darted out of the slipstream of his relatively inexperienced colleague to take the victory - four days after he showed his form by finishing second in the Brabantse Pijl semi-classic.
An emotional Gasparotto pointed to the heavens as he crossed the line before later dedicating his victory to his late team-mate Antoine Demoitie, the young Frenchman who was tragically killed in a crash during the Gent-Wevelgem classic earlier in the month.
Italy's Sonny Colbrelli (Bardiani Valvole) won the consolation sprint in the peloton four seconds adrift to take third place ahead of Frenchman Bryan Coquard (Direct Energie). Despite some impressive pacing by his Orica-GreenEdge team, Australian Michael Matthews, one of the pre-race favourites, could only take fifth place in what is viewed as the first race of 'Ardennes Week'.
Enrico Gasparotto wins Amstel Gold Race
How the race panned out
There was drama from the outset as Italy’s Fabio Felline (Trek-Segafredo) crashed in bizarre circumstances in the neutral zone at Maastrict after apparently catching his fingers in his spokes and being sent face first over the handlebars. Felline was taken to hospital for surgery on a broken nose but was said to be in a stable condition.
Once the race actually started it took time before a move came to fruition, an eleven-man group managing to extricate itself from the pack after 35 kilometres of racing.
The break - Laurens De Vreese (Astana), Tom Devriendt (Wanty-Groupe Gobert), Laurent Didier (Trek), Alex Howes (Cannondale), Matteo Montaguti (AG2R), Matteo Bono (Lampre), Kevin Reza (FDJ), Lawrence Warbasse (IAM), Josef Cerny (CCC), Fabien Grellier (Direct Energy) and Giacomo Berlato (Nippo) - managed to build up a maximum lead of just over four minutes before sunshine gave way to heavy rain.
The draining course of a succession of 34 short and sharp climbs took its toll and the break fragmented inside the final 50 kilometres. Meanwhile, a host of big name riders had been distanced by the peloton including triple winner Philippe Gilbert (BMC), rangy Dutchman Tom Dumoulin (Giant-Alpecin), Norwegian national champion Edvald Boasson Hagen (Dimension Data) and – perhaps most surprisingly – the defending champion, Michal Kwiatkowski (Team Sky).
Much of the damage was done on the Keutenberg with 30 kilometres remaining. It was cresting the steepest climb of the race that the gap of the remaining seven leaders – Howes, Warbasse, De Vreese, Devriendt, Montaguti, Bono and Grellier – came down to just 38 seconds.
Sky, who had led much of the chase, gave way to the Orica-GreenEdge team of Matthews, with last Sunday’s Paris-Roubaix winner Mat Hayman pulling hard on the front alongside Swiss rouleur Michael Albasini.
The remaining escapees were swept up with 15 kilometres remaining before Roman Kreuziger (Tinkoff) put in an attack on the penultimate climb, the Bemelerberg. The 2013 champion was soon caught and passed by Wellens, who managed to open up a sizable gap going over the summit.
Wellens held a slender 18-second gap at the foot of the Cauberg but it came crumbling down as soon as the pack shuffled in his wake. Gasparotto soloed past Wellens before being joined by the robust Valgren near the summit. Petr Vakoc, the Czech national champion and winner of last week’s Brabantse Pijl, was lurking but the Etixx-QuickStep youngster failed to bridge the gap.
As the gradient eased ahead of the 1.5-kilometre run to the finish, Gasparotto himself eased up and allowed Valgren to come through. 24-year-old Valgren proceeded to pull his companion well into the final few hundred metres of the race before Gasparotto inevitably danced on the pedals and took the win with relative ease.
With many of the big-name favourites – such as Gilbert, Kwiatkowski, Rui Costa (Lampre-Merida), Julien Alaphilippe (Etixx-QuickStep) and Joaquim Rodriguez (Katusha) – not hitting their expected heights, it was a podium that came very much from leftfield. But Gasparotto was a worthy winner, using his experience and form to take an emotional team for his Pro-Continental team Wanty-Groupe Goubert.
Ardennes Week continues on Wednesday with the Fleche Wallonne and next Sunday with the fourth monument of the season, Liege-Bastogne-Liege.