La Liga Results/Standings
Giuseppe Rossi had earlier given The Yellow Submarines a second-half lead amid heavy rain, but Valero's free-kick ensured that Villarreal had to settle for two draws in their opening two La Liga fixtures.
Soon after, Ariel Ibagaza sent Joesba Llorente clear on goal, but the former Valladolid man fired his shot low and it was easily blocked by the feet of Aouate.
Still, however, Villarreal came forward. Sebastien Eguren scooped an effort over the cross bar from inside the area, then Ibagaza, playing in place of the injured Marcos Senna, floated a free-kick inches wide of the target.
Mallorca’s forays forward were minimal, with a run and shot from Tuni that was easily gathered by Diego Lopez being the closest they came to breaking the deadlock.
As half-time approached, the heavens opened over El Madrigal, and a torrential downpour completely changed the playing conditions. Surface water left the pitch sodden and meant that slick passing was virtually impossible.
Indeed the water had left the pitch closer to a swimming pool, and the officials were left considering whether the match should be abandoned.
And the rainwater played a huge part when the opening goal eventually arrived from the boot of Rossi five minutes into the second half.
A pass infield from Capdevila caught in a puddle, and eventually the ball skidded through into the path of Llorente. As Aouate rushed from his line to block, the ball deflected into the path of Rossi, and the Italian drilled the ball home to give Los Submarinos Amarillos the advantage.
The former Manchester United forward should have perhaps doubled the lead minutes later, but could only manage a wild swing at a fizzing delivery from Diego Godin.
Despite this, it seemed that Villarreal would be able to see out the match and secure the win. However, they did not consider the conditions would come back to haunt them 15 minutes from time, as Mallorca converted an equaliser, against the run of play.
Borja Valero, making his first appearance upon his return from a spell in England with West Bromich Albion, swung in a dangerous delivery that skipped and slipped past everyone in the area, and fly past an unsighted Diego Lopez and into the net.
It was a poignant moment for the Islanders - it was their 1000th goal in top flight football in Spain, and although probably undeserved, put them in a strong position to take a point from the encounter.
Villarreal were perplexed - they had let their lead slip, and lay siege to the Mallorca goal in the closing stages in an attempt to reclaim it.
Both Santi Cazorla and Robert Pires stung the gloves of Aouate with powerful strikes, but the Israeli stopper stayed firm, and a frustrated Ernesto Valverde looked on from the home bench, knowing that his side had thrown away two points in the rain.
For Mallorca, however, four points out of six in the opening two matches represents an excellent start to the season for Gregorio Manzano's men.
Paul Macdonald, Goal.com