Mourinho arrived at Spurs last November and guided a struggling side to sixth and a UEFA Europa League place, but improvement was anticipated heading into the new campaign.

Tottenham was outplayed by Everton, though, which gave debuts to James Rodriguez, Allan and Abdoulaye Doucoure and might have led long before Calvert-Lewin's brilliant 55th-minute header.

Mourinho's men could not muster a response and are already searching for answers at the start of a brutal stretch in which they could play as many as nine matches before the October international break.

Everton was gifted a huge chance to take the lead after 16 minutes as Ben Davies's wayward cross-field ball escaped Toby Alderweireld and the alert Richarlison pounced.

The Brazil forward rounded Hugo Lloris but, with the angle narrowing, ignored Calvert-Lewin in the centre and awkwardly hacked over a gaping goal.

Jordan Pickford twice came to the visitors' rescue with big stops, turning Dele Alli's shot over the top and blocking from Matt Doherty, while James curled a 20-yard effort wide.

Mourinho replaced Alli with Moussa Sissoko at half-time, but Tottenham trailed 10 minutes after the restart as Calvert-Lewin towered over Eric Dier with a superb header from Lucas Digne's free-kick.

Richarlison twice bent attempts beyond the right-hand post, yet the single goal proved enough as Spurs struggled at the other end in a concerning early loss.

Tottenham goes next to Bulgaria before returning to visit Southampton next weekend. Everton, by contrast, has back-to-back home games against Salford City in the Carabao Cup and West Bromwich Albion in the league.