Coach Ernesto Valverde's men completed a league and cup double after thrashing Sevilla 5-0 in last week's Copa del Rey final, regaining the Spanish crown from Real Madrid and relegating Deportivo in the process. "But we take a lot of merit to win a title as hard as this without losing a game".
And the Portuguese striker, now 33, had his first goalless game in 13 on Wednesday in Real's 2-1 victory over Bayern Munich.
A defeat at this point could have unsettled their rhythm, but Ernesto Valverde's men dug deep to come away with a 2-1 win despite not being at their best thanks to Denis Suarez's 62nd minute leveler and substitute Paulinho's victor six minutes from time.
The Argentinian wizard's speed of thought and feet around the box helped him to yet another hat-trick - the 46th of his career.
It is the eighth time Barca have achieved the feat, although the celebratory parade through the city centre was not as well attended and less exuberant than in past years.
Last year, Iniesta became the first player to sign a lifetime contract with Barcelona, a deal that allowed him to keep playing for the club as long as he remained fit.
€2.5m settlement for terminally-ill woman whose cancer was missed
This morning the court was told the case had now settled and the case against the HSE could be struck out with no order. She revealed that Simon Harris had called her personally to apologise for the health service letting her down.
And they paid for those misses in the 38th minute when Barca netted a sumptuous second.
Barca knew they just had to extend their record unbeaten streak to 41 La Liga matches to seal a seventh title in 10 seasons, and Philippe Coutinho fired them into an early lead.
Struggling Deportivo came close to finding a victor and becoming the first team to beat Barca in the league this season.
Fourth-placed Valencia hosted Eibar but they could only draw a blank against the Basques.
The win over Espanyol was followed by a 3-0 Champions League victory over Juventus, showing Barca fans that their season was certainly not to be written off.
- responded well to conceding a 16th-minute goal from Paul Pogba. And they were hit badly as two late goals from Messi kicked them out of La Liga. Here, we pick out the top five.