And so the circle is completed. The first trophy Pep Guardiola won as the coach of Barcelona was the Copa del Rey with victory against Athletic Bilbao in 2009. On Friday night he took charge of his final match as Barça coach and defeated Athletic Bilbao to claim the Copa del Rey for a second time. Three years later this was his 14th trophy. He bows out as the most successful coach Barcelona have had.

Two first-half goals from Pedro Rodríguez and one from Lionel Messi made this a remarkably comfortable final. The difficult bit starts now, as the post-Guardiola era begins.

Barcelona had taken the lead after two minutes. Xavi Hernández's corner was headed on by Gerard Piqué and Javi Martínez was unable to control the dropping ball. It came off his thigh and into the path of Pedro, whose shot, though far from perfectly struck, found its way past Gorka Iraizoz. It had not even been Barcelona's first chance – Messi had already curled a shot fractionally beyond the post 27 seconds in – and it would not be the last.

Iraizoz made a sharp save from another Messi curler, again receiving on the right and coming inside on his left foot. And then Andrés Iniesta slotted Messi through in the inside-right channel. The Argentinian took a touch with his left foot and hit it high into the roof of the net at the near post. It was his 73rd goal of another astounding season. This was Messi's 14th final; it was the 13th in which he has scored.

Four minutes later Barcelona were 3-0 up. Xavi, Piqué and Pedro were again involved but the genesis of this could hardly have been more different from the first, Piqué striding out from the back, Xavi turning sharply and laying the ball off, Pedro curling his shot into the far corner.

There was a sudden flurry from Athletic and, with space opening up, from Barcelona too – a Pinto save, Messi's failed lob and Fernando Llorente's appeal for a penalty. It was a strong appeal too: turning Piqué, he appeared to have his shirt pulled and went to ground. The referee said no. Athletic's fans, easily a majority here, fell silent. It was happening again: two finals, two defeats. All that hope, all that illusion. Football, said Javier Mascherano before this game, has been unjust with the Athletic manager, Marcelo Bielsa. They had not deserved much more here but their season had.

The Argentinian coach has revolutionised Athletic Bilbao this season, changing their style and philosophy and leading them to two finals. Along the way they destroyed Manchester United; rarely had their supporters been so enthused – neutrals, too.

But they lost the Europa League final to Atlético Madrid and, looking both emotionally and physically burnt out, they collapsed in the final weeks of the league season, missing out on a Champions League place. Coming into this game they had not even scored for five matches. In Bucharest it finished 3-0. Here it was 3-0 before half time.

The second half simply drifted away, the end drawing slowly closer – both for Athletic and for Guardiola. Bielsa made two changes and the introduction of Ander Herrera especially gave bite and incision. He created the best chance for Ibai Gómez to chip over. There was a header, too, from Llorente but little else. In fact, the best moment was a Messi run from inside his half, past four players, which drew a sharp save from Iraizoz.

Eventually, the final whistle went – on this match and the Guardiola era. After the game, he said: "I am going to rest, then – I don't know when – if there is another challenge I will take it. I am tired. If I was on another bench I would [still] be tired."

Athletic: Iraizoz; Iraola, Amorebieta, Ekiza, Aurtenetxe; De Marcos (Herrera, h-t), Martínez, Muniain; Ibai, Llorente (Toquero, 73), Susaeta (Pérez, h-t).

Subs not used: Raul, San José, Gabilondo, Gómez, Iturraspe,

Barcelona: Pinto; Montoya, Piqué, Mascherano, Adriano; Xavi (Fábregas, 80), Busquets, Iniesta; Pedro (Thiago, 86), Messi, Alexis (Keita, 73).

Subs not used: Valdes, Bartra, Affelay, Cuenca.