Barca, the record winners, lead 3-1 from last month’s first leg at the Nou Camp, when their Brazil forward Neymar had a second-half penalty saved, and are closing on a 27th triumph in the competition.
They must be on their guard against one of the most entertaining teams in the top flight to secure a berth in May’s final against Athletic Bilbao or Espanyol who are level at 1-1 ahead of their second leg in Barcelona on Wednesday.
Luis Enrique’s expensively-assembled Barca were given a big scare by Villarreal at home in La Liga last month, twice falling behind before winning 3-2.
Villarreal spent a year in the second division in 2012-13 but have bounced back impressively under coach Marcelino and with a host of talented youngsters in the side have won praise for their attacking play.
As well as pushing Barca hard at the Nou Camp in La Liga, they fought back from a goal down to claim a point at Real Madrid on Sunday and inflicted a rare home defeat on champions Atletico Madrid in December.
Argentine forward Luciano Vietto scored the winner in that 1-0 win at the Calderon and is one of several talented youngsters under Marcelino’s command.
Russia midfielder Denis Cheryshev, on loan from Real, can score and create goals while the talents of Mexico forward Giovani dos Santos and his midfielder younger brother Jonathan, both products of the Barca academy, are undisputed.
Marcelino had warm praise for his players after Sunday’s game at the Bernabeu, singling out their professionalism and spirit of sacrifice.
“This draw tastes even better because it shows that with commitment and talent you can compete with any rival,” he told a news conference.
“We know the result from the first leg is against us and Barca’s enormous potential but we are not going to fail for a lack of effort,” added the 49-year-old who has had stints in charge at Sporting Gijon, Real Zaragoza and Sevilla.
(Editing by Tony Jimenez)