Primož Roglič (Jumbo-Visma) finally broke the Volta a Catalunya stalemate with a searing sprint to the top of Lo Port to snatch four seconds more in time bonus and another six seconds' of gap at the finish over rival Remco Evenepoel (Soudal-Quickstep).
The result put Roglič 10 seconds ahead of the World Champion Evenepoel with two stages remaining.
More drama came for the final podium spot, with João Almeida getting an assist from UAE Team Emirates teammate Marc Soler to take third on the stage and climb into third and Soler into fourth in the GC as both Mikel Landa (Bahrain-Victorious) and stage 2 winner Giulio Ciccone (Trek-Segafredo) faded from view.
Fifth on the stage, Rigoberto Uran (EF Education-EasyPost) moved into fifth in the overall standings with 19-year-old Lenny Martinez (Groupama-FDJ) a surprise finisher in sixth in both stage and GC.
"Happy," was how Roglič described his mood after the stage. "I'm still just coming back and it was a long time since I did this kind of effort in racing. I'm super happy. Like I said the first day, 300 or 500 metres of climbing was enough - but it's getting better and now I'm enjoying it.
"It's still two hard days to come. Not tomorrow probably but for sure the day after - three days and we'll do our best and see."
In addition to cementing his position atop the overall standings, Roglič leads the points classification and mountains classification, while Evenepoel is the best young rider.
The stage 5 summit finish at Lo Port, a hors-categorie ascent, capped off the 176.6-kilometre stage from Tortosa and was always going to be the most decisive stage, with the general classification a dead heat between jersey holder Primož Roglič and Remco Evenepoel after the first four stages.
The 160 kilometres before the final climb were punctuated by two categorised climbs, the Alt de Bot coming in the first 30km, the short but steep mid-stage Coll de Som and ended with 50 kilometres of flat roads to catch the early breakaway.
Three riders did not start: Quinn Simmons (Trek-Segafredo), Anders Halland Johannessen (Uno-X) and Oscar Riesebeek (Alpecin-Deceuninck).
It took the early breakaway some time to establish but when it did, it was a quality trio of climbing talent, with Guillaume Martin (Cofidis), Ethan Hayter (Ineos Grenadiers) and Tsgabu Girmay (Jayco-AlUla) who emerged ahead. Martin led the group over the top of the first climb with a 2:30 advantage on the peloton.
With Martin the best-placed 5:25 down, Jumbo-Visma had to keep the gap under control. There appeared to be an easing of the pace in the peloton when the gap got to four minutes as some of the Spanish riders were keen to join the leaders for TV time.
Hayter and Martin sat up on the long, gradual descent, with only the latter waiting for a chasing quartet, with Ibai Azurmendi (Euskaltel-Euskadi), José Felix Parra, Pablo Castrillo and Héctor Carretero (Kern Pharma), and Julen Amezqueta (Caja-Rural Seguros RGA) joining forces.
They eventually joined back up with Grmay, making seven up the road before the intermediate sprint in Mora la Nova with 103.5km to go. The gap fell just under two minutes as Lotto-Dstny came forward to hold the gap there.
After taking the maximum points atop the Coll de Som, Martin sat up, pleased to have padded his lead in the mountains classification.
Meanwhile, Soudal-QuickStep took up the task of closing down the escape group, which still held 2:30 with 22.6km to go. That gap fell rapidly under the pace of the Belgian team and as they hit the lower, unofficial slopes of the ascent to Lo Port.
Racing into the climb as if they were doing a sprint lead-out, Soudal-QuickStep's pace behind and the forcing of the two Kern Pharma riders whittled the gap down to a minute with 10km to go.
Grmay attacked with 9km to go, leaving Parra, Amezqueta and Azurmendi to chase as the gradient kicked up. Parra earned the most combative rider award but was quickly dropped as the single-file peloton stretched thinner and thinner and came closer and closer.
With 6.7km to go, Grmay was the last rider caught as Bahrain-Victorious led the peloton. As the lead group shrank, Evenepoel still had two teammates to Roglič's one, and they set a furious pace.
The gloves came off with 4.6km to go when Evenepoel launched off his teammate's wheel with Roglič and Soler the only riders to hold on. With teammate Almeida behind, Soler waited at the back and, with 2.2km to go, Almeida bridged across.
Looking to move up over Landa and Ciccone, Almeida surged in the last kilometre but failed to distance his two companions.
Roglič was next to accelerate but again, a stalemate until the road flattened and Evenepoel started his sprint. But it was too early and Roglič got the jump.
Stage 5 results
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