Bento took over from Shin Tae-yong in August in the wake of another early World Cup exit for the Koreans, who lost to Sweden and Mexico in their first two group games in Russia before stunning Germany 2-0 in their final match.
The Portuguese had overseen victories against Costa Rica and Uruguay, as well as a draw with Chile, and the Koreans were on track to record another win on Tuesday with a 2-1 halftime lead.
However, Panama pegged the hosts back thanks to some slack defending, giving Bento pause for thought ahead of friendlies against Asian Cup champions Australia and Uzbekistan next month.
"We don't have much time left until the Asian Cup, so it's important us to establish the foundation of this team," Yonhap News quoted him as saying. "We still have matches left in November, so we'll use those matches wisely."
While Bento is still searching for his best 11, one player he will not be able to call upon is Tottenham Hotspur forward Son Heung-min, who is unavailable until Korea's final group stage game in the United Arab Emirates.
Spurs had agreed to release the player for the 2018 Asian Games football tournament in the summer, which the Koreans won, on the condition that he missed the November friendlies and the first two matches of the Asian Cup.
Son said he would look to get back into peak condition at the Premier League side after a hectic 2018 and be at his best when he links up with the national team in January.
"I first need to recover well and stay in shape with my club," he said. "In that way, I'll be able to do well once I return for the national team."
South Korea, who finished runners-up to hosts Australia at the last Asian Cup in 2015, are grouped with China, Kyrgyzstan and the Philippines for the upcoming edition.
(Reporting by Peter Rutherford; Editing by John O'Brien)
