Doha: Roberto Mancini warned his Saudi Arabia players they face a "very difficult match" against South Korea next week in the Asian Cup last 16.
A lively but goalless draw with Thailand on Thursday – marked by four disallowed goals and a saved penalty – was enough for his team to top their group.
It sets up a clash in Qatar on Tuesday between two of the tournament favourites and a managerial face-off between two legends of the European game in Mancini and South Korean coach Jurgen Klinsmann.
Mancini's Saudi Arabia had already booked their place in the next round, as had Thailand, but Group F top spot was still up for grabs when they kicked off in Doha.
Saudi Arabia, who won their opening two games, were undefeated in their last 12 matches against Thailand in all competitions, with 11 wins.
And while they extended that run at the Education City Stadium, they could not turn their numerous chances into a winning goal.
South Korea won only one of their group games and were held 3-3 by minnows Malaysia on Thursday, but Mancini called them "a very good team", noting many of the Korean players are in top European leagues.
"We know it will be a very difficult match, not only for us, but also for them.
"Anything can happen," added the Italian.
His Saudi team had a chance to take the lead early against Thailand when they were awarded a penalty for a trip in the box.
But Abdullah Radif's tame effort was saved by Saranon Anuin, who was making his tournament debut in the Thai goal.
After that both sides had the ball in the net within two minutes of each other, but both were disallowed for offside.
Thailand added a third disallowed goal before half time, and the Saudis added a fourth after it.
In the 64th minute Mancini made a triple substitution which included the introduction of 16-year-old Talal Haji.
The Al-Ittihad forward provided industry up front but not a cutting edge.
As the game wore on Saudi Arabia created plenty of chances but always found a Thai defender in the way.
Thailand's third group-stage clean sheet makes them one of just two sides yet to concede in Qatar, the hosts being the other.
"If you want to get through in this competition you have to play against the top teams," Mancini said.
"You have to play Japan, South Korea, Australia, if you want to win."
In the other Group F match, Oman drew 1-1 with Kyrgyzstan and finish third. Both sides were eliminated.
Thailand finished second and face Uzbekistan next.