The fleet-footed midfielder, introduced at half-time at a festive Cartuja stadium in sweltering Seville, gave Spain the attacking flair they were missing in the first half and set up David Silva to score the 84th-minute winner after the home side had squandered a slew of chances and twice hit the crossbar.
Picking the ball up wide on the left, he surged past his marker into the area and pulled it back past stranded goalkeeper Zeng Cheng for Silva to sidefoot into the empty net.
Centre back Raul Albiol had rattled the frame of the goal with a header from a Fernando Torres flick at a 62nd-minute corner and Iniesta sidefooted the ball on to the crossbar after an audacious piece of close control a minute later.
"They closed the game down well in the first half but we woke up in the second and could have scored more goals," Silva said in a pitchside interview with Spanish TV.
"Andres made it very easy for me pulling the ball back and I just had to tap it in, he is a fantastic player," the Manchester City playmaker added.
The Spanish, who play their opening Group C match at Euro 2012 against Italy on June 10, would have won by a considerably wider margin had it not been for an inspired display by Cheng, easily China's best player.
The tenacious visitors, coached by former Spain boss Jose Antonio Camacho, made the brighter start and the home side narrowly avoided falling behind in a toothless first-half display from the world's top-ranked side.
WILD VOLLEY
Zheng Zhi rounded keeper Iker Casillas in the eighth minute after an uncharacteristic mistake by Xabi Alonso but fired his shot wide and the China captain then forced a brilliant save from his opposite number just before the half-hour.
Alvaro Negredo had Spain's best chance of the first period in the 10th minute but scuffed his shot straight at Cheng from Silva's low centre.
Spain coach Vicente del Bosque threw on players including Fernando Torres, Jesus Navas and Iniesta for the second half and the scoring chances started to flow as the world champions hogged possession.
A hungry-looking Torres, bidding to make the strikers' role his own in the absence of injured record scorer David Villa, volleyed wildly over from a Jordi Alba cross in the 67th minute and was then twice denied by Cheng before Silva fired straight at the keeper from close range.
China, ranked 66th, were ultimately overwhelmed by Spain's slick passing game and barely troubled Victor Valdes in the home goal after he replaced Casillas at the break.
Spain are bidding to become the first nation to win back-to-back continental titles with a World Cup in between at the European Championship in Poland and Ukraine.
