Madrid: Barcelona's outlay of 20 million euros ($22 million) on Jeremy Mathieu last July prompted plenty of criticism but the France centre back has been worth his weight in gold in the La Liga leaders' last two outings.

After scoring the opener in Barca's 2-1 win over second-placed Real Madrid in the 'Clasico' two weeks ago, Mathieu netted the only goal in Sunday's laboured 1-0 win at Celta Vigo that maintained the Catalan giants' four-point advantage over Real at the top.

Mathieu, who was signed to strengthen a defence that repeatedly let the club down last season, also put in an accomplished performance alongside Gerard Pique at the back as Barca kept their 16th clean sheet in 29 La Liga games this term.

‘I scored two important goals, I am pleased,’ Mathieu said in an interview with Spanish television.

‘Sometimes you have to suffer when you win,’ added the 31-year-old, who joined Barca after a five-year stint at Valencia.

‘It was a very tough match. After the international break it's more difficult as your rhythm always drops a bit.

‘Celta were the better team in the first half and in the second we benefited from a goal at a free kick. Sometimes you win in that way, when it's down to small details.’

Barca needed a win after Real romped to a 9-1 victory at home to Granada earlier on Sunday and are well placed to win a fifth La Liga title in seven years with nine games left.

Luis Enrique's side are also through to the last eight of the Champions League to face Paris St Germain and will play Athletic Bilbao in the King's Cup final at the end of May.

Victory in all three competitions would match the club's unprecedented treble in 2009 under Pep Guardiola.

‘It could be that we are fresher because a lot of players (in the squad) are used here,’ Mathieu said.

‘That is very important for the final stages of the season. We are on the right track and now we have to think about the next match.’

Barca have La Liga games at home to Almeria and away at Sevilla before they play at PSG in their quarter-final, first leg on 15 April.