Second-placed Real Madrid's 6-2 thrashing of Sevilla on Saturday had denied Barca the chance to win the championship in front of their own fans, but they showed few signs of nerves as they calmly dispatched their neighbors.
The Champions League finalists climbed to 91 points and restored their eight-point lead with three games left, needing only need a draw at Levante on Wednesday to wrap up the title unless Real slip up at home to Getafe on Tuesday.
Spain midfielder Iniesta slalomed his way into the area to beat Carlos Kameni at his near post after 29 minutes and his international teammate Pique nodded in at the near post from a corner just after the re-start.
One of the biggest cheers of the day for home fans was for Eric Abidal when the French fullback came on for the last 20 minutes as he continued his recovery from surgery on a liver tumor.
Earlier, Villarreal were held to a dull 0-0 draw at Real Mallorca, which damaged their chances of securing automatic qualification for next season's Champions League.
Juan Carlos Garrido's team, who were knocked out of the Europa League at the semifinal stage by Porto on Thursday, stayed fourth in the standings with 61 points and three games left after a rare midday kickoff.
Villarreal slipped five points behind local rivals Valencia in third, who were 3-0 winners over Real Sociedad on Saturday, but they pulled seven points ahead of fifth place.
Cristiano Ronaldo scored four goals in Real Madrid's win on Saturday.
Sergio Ramos, Ronaldo and Kaka all scored for Madrid in the first half on Saturday, and Ronaldo answered Alvaro Negredo's goal for Sevilla with a second-half hat trick before Negredo added another one late on.
It was the second time Ronaldo has scored four goals this season after his haul against Racing Santander on Oct. 23.
He now has a leading 33 goals this season, two more than Barcelona forward Lionel Messi.
Barcelona will instead look to restore its eight-point lead over Madrid when it hosts Espanyol in the Catalan capital derby.
"The longer it takes Barcelona to win the league, the better," said Ronaldo. "We have to win all the games we can without thinking about Barcelona." All of Spain's topflight matches - except for the game at Sevilla - began after a minute's silence in memory of Seve Ballesteros, the Spanish golf great who died in the early morning.
Sevilla was completely outclassed at Sanchez Pizjuan stadium and failed to manage a single shot on goal before halftime.
"Against this team the danger is to become desperate and leave spaces behind, that is one of their virtues," said Sevilla coach Gregorio Manzano, who also asked Sevilla's fans for their forgiveness for his team's poor performance.
Madrid showed none of the struggles in attack that led to its elimination by Barcelona from the semifinals of the Champions League earlier this week, with the exhausting four-game series between the two Spanish giants finally having drawn to a close.
Jose Mourinho's team wasted no time in taking out its European frustrations on Sevilla with an attacking starting 11 that included Mesut Oezil and Karim Benzema up front along with Ronaldo and Kaka.
