Villarreal missed the opportunity to put real pressure on the top four after picking up a draw at Abanca Balaidos on Friday night.
The Yellows took an early lead in Galicia through Gerard Moreno but ultimately conceded an equaliser and had to hold on for dear life to take a point back to Castellon.
Villarreal looked like the side they have been under Quique Setién over recent weeks during their five-game winning run in the first half, but the second half saw a tired performance that they were punished for - and it could have been worse.
Villarreal started strongly and took the lead in the 15th minute when Gerard Moreno produced a moment of brilliant. Receiving the ball from Samu Chukwueze, he turned out of pressure and half-volleyed into the bottom corner from 25 yards or more in just two touches.
The Yellows continued to dominate in the first half, but as is the way in this new style, they were a little open, and Aissa Mandi had to produce a heroic block to keep out the hosts.
The second half played out very differently, with Villarreal looking a shadow of their first-half selves. Pressure dropped off, and aside from a Jose Luis Morales strike that glazed the crossbar, the Yellows showed very little in attack.
Jorgen Strand Larsen took advantage of one of Celta’s attacks, with Pau Torres caught sleeping. Larsen ghosted in behind to latch on to a through ball and finish.
Villarreal lost Juan Foyth to an apparent shoulder injury after an awkward landing, and Kiko Femenia was brought off before being replaced just minutes later, with Setién seemingly realising he had made a mistake, bringing on Jorge Cuenca instead.
Unai Nunez came close to winning it with around eight minutes remaining, heading just wide from the penalty spot, Pepe Reina proved particularly important throughout the night, too, with the veteran showing why the Yellows won’t be missing Geronimo Rulli, even if they don’t get a replacement.
Villarreal hung on in the end and took a point back to the East of Spain, and they now turn attention to a Copa del Rey clash with Real Madrid during the week.