In 2014, it was announced that Po-on would be the head coach at Chiangrai United for the next season, after retiring from professional football on the same day.
On 5 February 2023, Teerasak returned to Nakhon Ratchasima, agreeing a two-year contract to replace outgoing manager Kevin Blackwell.
His first game in charge was a Thai FA Cup match on 8 February 2023 against Suphanburi, ending with a 5–1 victory for Nakhon Ratchasima.
On 21 April 2023, a Thai League 2 match against Nongbua Pitchaya ending with a 3–0 victory for Nakhon Ratchasima.
As a result, the team won the Thai League 2 championship in the 2023–24 season, even though the last match was left to play against Chanthaburi because Nakhon Ratchasima had a better Head To Head result than Nongbua Pitchaya and was considered the first champion in 10 years for the team.