The Movistar rider outlasted a select group of 30 riders as he ground its way up the 9.6 percent gradient and kicked to finish ahead of Julian Alaphilippe (Etixx-Quick-step) and Michael Albasini (Orica-GreenEDGE).
Valverde now joins Belgians Eddy Merckx and Marcel Kint as well as Italians Davide Rebellin and Moreno Argentin as triple Fleche champions.
“There's no secret. You just need to be in great shape and to love these races. There's not a secret, just a lot of training. To match a rider like Eddy Merckx is great. It gives me a lot of confidence and it shows that at 35, soon, I still have the legs to perform well.” - Alejandro Valverde.
Thomas De Gendt (Lotto-Soudal), Pieter Van Speybrouck (Topsport Vlaanderen-Baloise), Jerome Baugnies (Wanty-Groupe Gobert), Reinier Honig (Roompot Oranje Peloton), Daniele Ratto (United Healthcare), Mike Teunissen (LottoNL-Jumbo) and Brice Feillu (Bretagne-Séché Environnement) were the seven riders who were allowed to organise an escape after just eight kilometres.
Their resistance was effective as they managed to build a time gap of seven minutes and 40 seconds on the peloton. But with the majority of kilometres completed the group lost Theunissen and Honig on the Côte de Bellaire and was completely reined in after the first pass of the Mur de Huy.
While the break was resisting the efforts of the peloton, the final 40km was marred by a series of crashes which claimed several riders, including BMC’s Philippe Gilbert and Chris Froome (Sky). Gilbert abandoned but Froome continued to finish.
"It was a very tense race indeed with crashes already 130kms before the finish and crashes that occurred in the first 30 positions of the pack." - Alejandro Valverde.
With Gilbert out, BMC enacted an ill-fated Plan-B, sending Tejay van Garderen in chase of the new leaders Giovanni Visconti (Movistar) and Luis-Leon Sanchez (Astana).
However, Van garderen was never allowed much leeway and Visconti and Sanchez were caught with 6kms to go. Immediately Tim Wellens (Lotto Soudal) briefly took the lead as the peloton massed itself for a final assault on the Mur de Huy.
Flèche Wallonne: 205.5kms, Waremme - Mur de Huy
1 Alejandro Valverde (ESP) Movistar 5hr 08min 22sec
2 Julian Alaphilippe (FRA) Etixx-Quick-Step
3 Michael Albasini (SUI) Orica-GreenEDGE
4 Joaquim Rodriguez (ESP) Katusha
5 Daniel Moreno (ESP) Katusha
6 Alexis Vuillermoz (FRA) AG2R 0:00:04
7 Sergio Luis Henao (COL) Sky
8 Jakob Fuglsang (DEN) Astana
9 Tom Jelte Slagter (NED) Cannondale-Garmin
10 Wilco Kelderman (NED) LottoNL-Jumbo