Arsenal saw off highly-fancied Napoli 2-0 at the Emirates, while Marco Alonso's late header earned Chelsea a hard-fought win at Slavia Prague.
Manager Maurizio Sarri is in danger of being sacked after a dismal first season at Stamford Bridge.
Alonso has made 92 appearances and scored 15 goals for Chelsea since being signed from Fiorentina.
Chelsea's second successive win under new boss Maurizio Sarri lifted them to the top of the Premier League with a 100 percent record.
Alvaro Morata struck his 10th goal of the Premier League campaign as Chelsea secured a 2-0 victory over Brighton that moved Antonio Conte's side to within one point of second-placed Manchester United.
Marcos Alonso struck the winner with less than three minutes remaining in an impressive show of character by Chelsea, after they had been pinned back when substitute Michy Batshuayi headed into his own net eight minutes from time.
The win over Middlesbrough left Chelsea seven points clear of Tottenham Hotspur at the summit and means they will be crowned Premier League champions for the second time in three seasons if they win at West Bromwich Albion on Friday.
David Luiz is a beneficiary of the Premier League's first billion-pound spend, and is back just two years after he became the world's most expensive defender with a 50 million pound move to Paris Saint-Germain
Real Madrid says former defender Marcos "Marquitos" Alonso Imaz, who helped the club win a record five straight European Cups, has died. He was 78.
Bolton Wanderers' Spanish left back Marcos Alonso has been detained for questioning in Madrid after a car he was driving while allegedly under the influence of alcohol was involved in a deadly car accident, Spanish media reported on Monday.
