On April 30, 2016, he secured a 1st-round KO victory over Brazil's Reinato Gomes at THAI FIGHT Samui 2016. On July 23, 2016, Tengnueng would brutally dispatch Sok Tauch of Cambodia with a 1st-round TKO victory at THAI FIGHT Proud To Be Thai.. On August 20, 2016, Tengnueng was able to secure 2 KO wins in one night at THAI FIGHT KMITL. He first knocked out Yan Naing Aung of Myanmar in the 1st round. He then proceeded to deliver another 1st-round KO over Sinan Uluturk of Turkey that same evening. At THAI FIGHT London, on September 11, 2016, he beat Sam Gough by 1st-round TKO with a low kick. On October 5, 2016, Tengnueng defeated Erik Massion of Germany by 1st-round KO at THAI FIGHT Emei. He would then go on an uncharacteristic three-fight losing streak, including a decision loss to Hamza Ngoto at THAI FIGHT Paris on April 8, 2017. This marked his first loss in THAI FIGHT since September 19, 2012. After a period of inactivity for most of 2017 and 2018, in which he fought once each year, Tengnueng later returned to THAI FIGHT in 2019 on February 23, 2019 at THAI FIGHT Phuket 2019. This time, he had noticeably put on weight and fought at a heavier 80 kg (176 lbs), as opposed to his previous fighting weights of 70-75 kg (154-165 lbs). His first opponent of the year was Russia's Mike Vetrila, whom he knocked out in the 1st round, keeping his streak of KO wins alive at 12. On March 30, 2019, he defeated Evgenii Afanasev at THAI FIGHT Mueang Khon 2019 by 2nd-round KO. Tengnueng seemed to return to his previous form, despite his weight gain, when he delivered a 1st-round KO of Simon Maait of Australia at THAI FIGHT Samui 2019 on April 27, 2019. However, this was not to last as his performance was called into question when he faced Mohammad Hossein Doroudian of Iran at THAI FIGHT Betong 2019 on June 29, 2019. After uncharacteristically getting knocked down early in the 1st round, Tengnueng seemed hesitant to engage but was able to inflict his own damage in much of the 2nd round.