The Thais had already won Pool A, winning all three matches to end the group stage with a perfect 9-0 win-loss record, to set up a clash with Indonesia, who topped Pool B.
National team debutant Pawit Sornlaksup claimed the first point for Thailand in the play-off match when he defeated Lucky Candra Kurniawan 6-2, 6-2 at Hanaka Paris Ocean Park.
Kasidit Samrej battled past Nathan Anthony Barki 7-6 (7/4), 6-7 (9/11), 7-6 (7/2) in a match that finished at 3am on Sunday morning after a seven-hour rain delay to wrap up the tie.
“All the praise must go to the players, especially Kasidit who kept on fighting until we won the second singles and the tie,” said captain Patcharapol Kamsaman.
“Today’s tie finished at nearly 3am but every player had a good mentality and kept on cheering their teammate on. It was not easy and the players showed their fighting spirit,” he added.
Thailand had already secured a place in the Davis Cup World Group II Playoffs next year after they beat Saudi Arabia to claim the top spot in Pool A of the Asia/Oceania Group 3 on July 17.
Heading into the tie level on top of Pool A standings with two wins, the Thais proved too strong for their Saudi opponents, to compete a 100% group win record.
Pawit Sornlaksup defeated Bader Idrees 6-0, 6-0 in the first singles match before Kasidit Samrej beat Abdulmajeed Bukhari 6-2, 6-1 to give Thailand a 2-0 lead.
The doubles match between Pruchaya Isaro and Maximus Jones and Idrees and Bukhari lasted just three games before the Saudi pair retired at 2-1 with Idrees suffering a leg injury.
Thailand and Indonesia earned spots in next year’s World Group 2 playoffs after winning their respective pools.
They are joined by Syria, who beat Saudi Arabia 2-1 in a promotion playoff between the two teams.