Chelsea goalkeeper Emiliano Martinez left the pitch on a stretcher with a serious-looking head injury as Xabi Alonso’s side won at Everton.
Argentina World Cup winner Martinez and Everton defender Jarrad Branthwaite clashed heads as they went for the ball in the 75th minute.
Branthwaite was able to continue after treatment, but the game was held up for 10 minutes as Martinez received medical care.
The 34-year-old, who was able to move his arms as he was carried off, was replaced by Mike Penders.
The game was settled by two goals from wing-back Pedro Neto, who scored at both ends of the second half.
He netted his first from Jorrel Hato’s deflected cutback, then added a late second with a cool rolled finish into the bottom corner after Jordan Henderson’s free-kick hit the wall.
The result gave Chelsea a first Premier League clean sheet in nine months and was Everton’s first league defeat this season.
Chelsea go fourth, with Everton sitting sixth, before the rest of the weekend’s games.
Neto scored his first double in a Premier League game in what was his 187th appearance in the English top flight, but the focus was not on him at the full-time whistle.
The Portuguese showed good composure for both goals, which came in the opening minute of the second half and then the 90th minute, with 11 minutes added on after that.
Chelsea were good value for the win and threatened to add to their tally, most notably when Moises Caicedo’s stunning volley hit the angle of post and crossbar.
Cole Palmer had six shots, including a clever lob from Morgan Rogers’ through ball which landed on the roof of the net.
They will now wait for news of the injury affecting keeper Martinez, who went straight to hospital after being carried off the pitch. Belgian Penders, 21, made his Premier League debut when he came on.
Between them, the two goalkeepers helped Chelsea to their first clean sheet in the league since 17 January, ending a run of 22 games with conceding.
The Toffees, at kick-off, were one of three unbeaten teams in the Premier League, along with Manchester City and Brentford, although four of those six games were draws.
But they could not equal their longest undefeated start to a Premier League season – when they managed three wins and four draws in their opening seven games of 2006-07.
They did have chances with the game goalless, most notably Thierno Barry’s close-range header which was straight at Martinez.
Everton’s only senior striker has attempted more shots than anybody else this season in the Premier League – 25 – but has only scored three times.
There were several flashpoints in the first half, with five bookings – and Everton felt Morgan Rogers should have been given a second yellow for a 50-50 with James Garner.
But once Chelsea scored, David Moyes’ home side never looked like coming back, and they only had two shots in the second half.
