Antonio Conte has warned David Luiz he faces a battle to regain his place in the first team after dropping the centre-half for the champions’ critical victory over Manchester United, a win that left the visitors eight points adrift of the top.

Álvaro Morata’s second-half header proved the decisive moment at Stamford Bridge but David Luiz, such a key player in Chelsea’s Premier League title triumph last season after rejoining from Paris Saint-Germain, watched the game from behind the home dugout with Conte claiming his omission was born of shoddy recent form. The Brazilian’s replacement, the Danish youngster Andreas Christensen, performed impressively as Chelsea moved to within a point of United, albeit still nine from Manchester City at the top. The 17-year-old midfielder Ethan Ampadu, who has yet to feature in the top flight, had been included instead among the substitutes. Asked afterwards whether David Luiz had a future at the club, Conte said: “I don’t know. He has to work really hard, otherwise they are on the bench or in the stand.” The Italian was subsequently asked to clarify those comments, and added: “It’s very simple, no? Very simple. The coach has to make the best decision for the team and tonight the best decision for the team was to play with Christensen and to have, on the bench, [Ethan] Ampadu. Another young player. A really good player for the present and the future.

“Maybe in the future I can decide a different way or continue in this way. That’s normal. I must take the best decision for the club, not for a single player. It’s only a tactical decision. It’s normal. This can happen to every one of my players, if I see they are not in good form. It’s normal. I repeat: I have to put my face to every situation and then sometimes to make important decisions. Today I did this and I think Christensen played a massive game. I was very happy for this.”

David Luiz’s omission came only a few weeks after Conte had described him as his best defender at the club. “But it can change, it can change,” he said, with the Brazilian having been omitted from the final training session before United’s visit. He had clashed with Conte over his early substitution during the Champions League home game with Roma last month. The Brazilian must now prove he warrants inclusion in the side that travels to West Bromwich Albion after the international break by impressing in training over the next fortnight.

The Italian praised his team for playing “with great energy, with great passion, with great enthusiasm” to record a third successive Premier League win and erase some of the painful memories of the midweek capitulation in Rome.

There was disappointment for his opposite number, José Mourinho, on his latest fruitless return to Stamford Bridge, with the Portuguese left to contemplate falling further behind in the title race. . “We are worried [about the gap] but there are 18 teams more worried than us because we are second,” he said. “Eight points, in the Premier League, is not the same as eight points in the Portuguese league, La Liga, the Bundesliga. Here, there’s still a lot to play [for]. I hope, I feel, I think, I wish that in the busy period of late November, December, beginning of January, I think probably we are going to be at our maximum strength with Paul Pogba, Marcos Rojo and Zlatan Ibrahimovic back. So, probably, we can be on a high.”

The United manager had waited to shake hands with Conte near the mouth of the tunnel after the match, only for the Italian to celebrate instead on the pitch with his victorious players. “You want me to go and chase him in the middle of the pitch?” added Mourinho. “I was there. I shook hands with the people who were there. I think one of them was his brother, the assistant, so I feel that by shaking the hands of his brother and the other assistants that I did my duty. I cannot go and run to chase him.”