Chelsea suffered a humbling 4-1 defeat to Celtic in Indiana on Saturday, with Enzo Maresca’s side struggling to contain the Scottish team’s attacking prowess at Notre Dame Stadium.

Matt O’Riley, Kyogo Furuhashi, Luis Palma, and Michael Johnston found the net for Celtic, with a late Christopher Nkunku penalty providing a consolation goal for the Blues.

This was Maresca’s second pre-season outing as Chelsea’s manager, and his tactics were exposed by the Hoops.

His first game in charge was a 2-2 draw against Wrexham earlier in the week.

Here are five key takeaways from the action.

Chelsea’s high line was easily breached

Celtic repeatedly exploited Chelsea’s high defensive line with long balls over the top, which led to several scoring opportunities.

This tactic was reminiscent of Tottenham under Ange Postecoglou last season, and it’s an area Maresca needs to address quickly.

Chelsea’s right-hand side was particularly vulnerable, especially when Reece James ventured into midfield, leaving a gaping hole behind him.

This was Enzo Maresca’s second game in charge of Chelsea and things must get much better

Nkunku shone in an otherwise dismal display

One of the few positives for Chelsea was the lively performance of Christopher Nkunku, who looked sharp and played the full 90 minutes.

The Frenchman carried a threat across the front line and was the only player to complete the full match.

Marc Guiu also impressed, showing his ability to handle the physicality of the Premier League.

The 18-year-old Spaniard is getting his chance to shine, and it’s up to Maresca to decide whether to send him on loan or keep him in the first team.

Christopher Nkunku was one of Chelsea’s better performers and scored his side’s only goal of the match

Schmeichel still has it

Kasper Schmeichel, who joined Celtic on a free transfer, showed he still has what it takes to be a top goalkeeper.

The 37-year-old made several impressive saves, including back-to-back stops to deny Nkunku and Carney Chukwuemeka.

Chelsea, meanwhile, are close to signing Villarreal’s Filip Jorgensen for £20.7m on a seven-year contract.

Jorgensen will provide competition for Robert Sanchez, with Djordje Petrovic potentially being sold.

Sanchez made one sensational save but looked shaky when trying to play out from the back.

Former Man City and Leicester goalkeeper Kasper Schmeichel proved he was still pivotal between the sticks

Chelsea won’t face pitches this bad all season

The playing surface at Notre Dame Stadium was far from ideal, but Chelsea won’t have to deal with pitches this bad all season.

Cole Palmer, Conor Gallagher, and Marc Cucurella will not join Chelsea’s squad in the United States, but that’s not the worst news, as it keeps them away from these pitches.

The ball was constantly stalling on the pitch, which didn’t help Chelsea’s pass, pass, pass style of play.

But that’s no excuse for being embarrassed by Celtic.

The playing surface at Notre Dame Stadium was far below the standards Chelsea are used to

Mistakes will happen

When Pep Guardiola took over Manchester City, they made mistakes as they adapted to his tactics.

The same will happen with Chelsea over the next season as they implement Maresca’s style of play.

Already, we’ve seen a howler in pre-season, and Chelsea supporters best get used to having hearts in mouths at Stamford Bridge.