Gloucester held off a spirited Castres side to reach the last eight of the European Challenge Cup.

They will face either Sale or Ospreys in a home quarter-final after first-half tries from Zach Mercer, Jonny May and Max Llewellyn put them in control.

Castres rallied as Loris Zarantonello and Josaia Raisuqe went over in the second half but Gloucester stood firm.

The Cherry and Whites have already marked their 150th anniversary by adding England's domestic cup to their cabinet by beating Leicester last month, but they are now eyeing a European final at the Tottenham Hotspur Stadium on 24 May.

As second seeds, they are guaranteed home ties all the way to the final should they get there and Castres were the latest to succumb to their fine cup form.

The French side were beaten 35-5 by Gloucester in a dead-rubber group game in January but were considerably stronger this time around, with 11 changes from that starting line-up.

And they showed plenty of intent as full-back Julien Dumora started and finished a pacy attack within three minutes to give the visitors the lead.

Gloucester rumbled into action and kept the ball alive three times in a rampaging attack down the right flank for Mercer to race over and level the score.

Gloucester spurned a kickable penalty to kick for the right-hand corner and when they quickly shifted the ball left from the line-out, May shot through a gap to put them ahead.

The impressive Mercer again ensured quick ball from a line-out to feed Llewellyn, who burst through three tackles to power over, and with Santi Carreras converting all three in windy conditions, Gloucester had some daylight.

Pierre Popelin's two penalties ate into the lead but Carreras replied in kind with two of his own as Gloucester sought to see out the game.

Castres roused themselves for a big finale as Zarantonello went over at the back of a driving maul to close the gap to seven points.

Another Carreras penalty settled any anxiety, and Raisuqe's try from another maul was too late to affect the result.

Line-ups

Gloucester: Carreras; May, Llewellyn, S. Atkinson, Thorley; C. Atkinson, Varney; Ruskin, Socino, Gotovtsev, Clarke, Thomas, Ackermann, Ludlow, Mercer.

Replacements: McBurney, Vivas, Ford-Robinson, Jordan, Tuisue, Clement, Chapman, Harris.

Castres: Dumora; Raisuqe, Dupont, Goodhue, Nakosi; Popelin, Doubrere; Walcker, Barlot, Azar, Pieterse, Vanverberghe, Delaporte, Maravat, Peysson.

Replacements: Zarantonello, de Benedittis, Chilachava, Nakarawa, Babillot, Fernandez, Seguret, Chabouni.