Membrado began the final day with an 8.9sec advantage, but that margin disappeared on the opening 30.02km pass through Himos–Jämsä.
Lassila delivered the attack expected from the local driver, going 12.1sec faster than Membrado and turning his overnight deficit into a 3.2sec lead with only the Wolf Power Stage remaining.
Calle Carlberg was fastest on the stage, edging Lassila by just one-tenth of a second despite surviving a sizeable moment near the finish. Ali Türkkan followed in third, 2.0sec off the pace, after reporting that he had become caught in Kerem Kazaz’s dust.
Kazaz, meanwhile, adopted a deliberately cautious approach as he protected fourth place, admitting that there was little to gain and plenty to lose by taking unnecessary risks.
The focus, however, was firmly on the battle at the front.
With more than 30 competitive kilometres remaining, Membrado needed to beat Lassila by over three seconds on the Finn’s home roads to recover the victory.
The Spaniard responded emphatically.
Membrado completed the second Himos–Jämsä pass in 15min 11.921sec, setting the fastest Junior WRC time by 4.394sec over Türkkan. Lassila was a further 0.830sec back, surrendering the lead and finishing the rally just 2.0sec behind.
“This is just an incredible feeling,” said Membrado.
“In the weeks before, my mind was stressed, thinking if I was good enough to win in WRC. But this means yes. I did a really good push and I’m really, really proud of myself.”
Lassila was left to settle for second after coming within one stage of a home victory, while Carlberg completed the podium 1min 04.7sec behind the winner.
Kazaz brought his Ford Fiesta Rally3 home fourth and 2min 31.9sec back, with Türkkan fifth after a weekend affected by a crash on Friday, a puncture on Saturday and 20sec in penalties.
Despite finishing fifth, Türkkan was the rally’s most prolific stage winner. The Turkish driver claimed eight fastest times, ahead of Carlberg with four, Lassila with three, Membrado with two and Kazaz with one.
Those stage-win bonus points ensured the championship fight remains finely balanced heading towards the finale.
Carlberg continues to top the standings on 95 points, but Türkkan is now only three behind on 92. Membrado’s victory lifts him to third on 71, ahead of Lassila on 61, with Raúl Hernández fifth on 36.
The Junior WRC title will be decided at Rally Chile Bio Bío, where double points will be available at the fifth and final round of the season.