Lionel Messi says Argentina have "no excuses" after they fell to a hugely disappointing 2-1 loss to Saudi Arabia in their World Cup opener at Lusail Stadium on Tuesday.

Argentina headed into the tournament as one of the favourites to win their third title, and a Messi penalty put La Albiceleste a goal to the good at half-time as they appeared to be cruising to a first victory in Group C.

However, two goals in the space of five minutes from Saleh Al Shehri and Salem Al Dawsari completely flipped the script, and Messi's side were condemned to one of the biggest shocks in World Cup history.

Messi acknowledged he and his team-mates must not seek to justify the stunning loss, though he hoped it would end up bringing the group closer together.

"There are no excuses," Messi told reporters in a post-match news conference.

"It's a very hard blow for everyone, we didn't expect to start like this.

"We are going to be more united than ever. This group is strong and they have shown it.

"This is a situation that we did not have to go through in a long time. Now we have to show that this is a real group.

"Things happen for a reason. We have to prepare for what's coming, we have to win and it depends on us."

After Messi converted from the spot to put Argentina 1-0 up after just 10 minutes, Lionel Scaloni's men remarkably saw three goals chalked off for offside before half-time as Saudi Arabia employed a bravely high line.

The Paris Saint-Germain star complimented Herve Renard's side for their defending, but conceded Argentina could have done more to break through.

Messi said: "We knew that [Saudi] Arabia is a team with good players, that moves the ball well and that advances the [defensive] line a lot.

"We had worked on it, but that's why we had many goals ruled out. Perhaps we did not find the right moment to avoid falling into the trap."

The defeat ended a run of 36 matches unbeaten, and Messi feels La Albiceleste need to get the fundamentals right to bounce back and salvage their World Cup campaign.

"It's the first game," Messi added. "It's up to us to correct what we did wrong, [and] try to get back to the base of who we are."

Argentina now face Mexico in a crucial clash on Saturday, before their group stage ends against Poland on November 30.