Park was one of the two assistant managers of Guus Hiddink at the 2002 FIFA World Cup. In August 2002, Park was appointed as head coach of the South Korean under-23 side for the 2002 Asian Games by performing successfully as the senior team assistant. However, Korea Football Association had not done any preparation for the 2002Asian Games since there was no manager or coaching staff for two years. KFA had focused on the 2002 FIFA World Cup, which was co-hosted in South Korea, so Park had to prepare for the tournament in two months. In addition, KFA was criticized that Park worked without getting paid because they formally didn't sign with him. South Korea lost to Iran after penalty shoot-out in the semi-finals, and later won a bronze medal. Park was sacked after the tournament.
Coaching in South Korea
In August 2005, Park became the inaugural manager of the newly-formed Gyeongnam FC in the K League. Gyeongnam finished fourth in the 2007 K League season, but Park left the team due to internal conflict. In December 2007, he succeeded Huh Jung-moo as coach of the Chunnam Dragons. The team finished as the runners-up of the 2008 League Cup and sixth in the 2009 K League. He later resigned due to poor performances in the 2010 season. From 2012 to 2015, Park coached the military team Sangju Sangmu FC in South Korea. Under his guidance, his squad won the country's second-division league, K League Challenge, in 2013 and 2015. He left the team after his contract expired after the 2015 season. In 2017, Park was appointed manager of Changwon City FC, a third-division team. Changwon won the 2017 Korea National League Championship, and he was named the tournament's best manager.
Vietnam national teams
On 29 September 2017, Park was appointed the head coach of the Vietnam national football team. Also in charge of the under-23 side, the team reached the final of the 2018 AFC U-23 Championship, which is Vietnam's first final in the official AFC competitions. At the 2018 Asian Games, the under-23 side also advanced to the semi-finals and finished fourth for the first time in 56 years, with Park earning praise for his management. On 15 December 2018, the Vietnamese team under Park won the AFF Championship after defeating Malaysia, 3–2 on aggregate, in the second leg of the finals in Mỹ Đình National Stadium of Hanoi. This was Vietnam's first regional championship in ten years. In the 2019 AFC Asian Cup, Vietnam reached the quarter-finals but lost to eventual runner-up Japan, 1–0. On 6 November 2019, Park had extended his contract to coach the Vietnam and the under-23 team until 2022. With the under-22 squad, Park won the gold medal at the 2019 Southeast Asian Games, thus winning the first football title for Vietnam as a united country at the games as Vietnam previously lost in the final on five occasions.
Park is a devout Methodist Christian. While coaching Vietnam, he was nicknamed "Coach Terminator" by the Vietnamese media, due to his tendency of defeating a number of notable managers and, directly or indirectly, forcing them into being sacked. Managers that were sacked or resigned for losing to Park's Vietnam include Guus Hiddink, Ján Kocian, Sven-Göran Eriksson and Bert van Marwijk.
