Tuchel replaced Lampard following a disappointing start to the 2020-21 Premier League campaign.
Chelsea were ninth when the German was appointed and a near-impeccable run of form meant that they finished fourth.
That success has led to the West Londoners being considered one of the favourites to win the Premier League this season. The club has not won England’s top-flight since 2017.
A sensational double save kept Aston Villa at bay last weekend. It helped to set up a 3-0 win, sealed largely thanks to Romelu Lukaku’s brace.
Mendy believes that a club having two good goalkeepers can provide a strong platform for success. He insists that competition with Arrizabalaga and Marcus Bettinelli, was a a free transfer signing from Fulham, is strong.
The Senegal international continued: “You can see it at Manchester City and at Liverpool – two good goalkeepers who are ready to play.
“So you have to be the best for yourself but for the team also because when the coach puts you on the pitch, you have to show why he called you.
“Every time you have to show it, and you have to push each other at training. It’s competition and Kepa, me or Marcus [Bettinelli], we want to be the best for the team.”