The top seed and Olympic champion picked up a 21-18, 21-12 win on day four of the BWF World Tour Super 300 event at the Pavelló de la Vall d'Hebron.

Marín spent eight months on the sidelines last year after suffering an anterior cruciate ligament injury, but she has been working her way back to her best form as Tokyo 2020 approaches.

Standing between her and a place in the final is another Thai player, Supanida Katethong, who defeated Chinese Taipei's Chiang Ying-li 21-19, 16-21, 21-17.

The other semi-final encounter will be an all-Thai contest between third seed Busanan Ongbamrungphan and sixth seed Pornpawee Chochuwong.

Ongbamrungphan overcame India's Saina Nehwal 22-20, 21-19, while Chochuwong beat Turkey's Neslihan Yigit 22-20, 21-9.

In the men's singles event, reigning champion Viktor Axelsen of Denmark brushed aside compatriot Jan Ø. Jørgensen in just 25 minutes to reach the semi-finals.

Axelsen, the 2017 world champion, cruised to a 21-8, 21-5 victory to edge closer to the successful defence of his title.

Next up for the 26-year-old is set to be unseeded Liew Daren after the Malaysian fought back from one game down to claim a shock 16-21, 21-17, 21-17 win over Denmark's Rasmus Gemke, the fifth seed and winner of the event in 2018.

The other penultimate-round match will see India's Ajay Jayaram face Thailand's Kunlavut Vitidsarn.

Jayaram defeated France's Thomas Rouxel 21-14, 21-15, while Vitidsarn came from behind to overcome India's Sameer Verma 17-21, 21-17, 21-12.

Action in Barcelona is due to continue tomorrow.