[3] In the 1998–1999 cycle, Antonio (2540) tied for 1st-4th places in the Zonal 3.2a held at Yangon in December 1998 with Super GM Adianto (2610), IM Dede Liu (2375) of Indonesia and FM Dashzeveg Sharavdorj (2385) of Mongolia that necessitated a play-off among the 4 players as all 4 scored 6.5/9 with Antonio posting 5 wins, 3 draws and 1 loss with a TPR of 2565 in the 30-player field.

[4] In the ensuing playoff, Antonio came out on top with 4.0/6 (+2 =4 -0) as he qualified for the 1999 World Championship held at Las Vegas.

[30] Antonio (2573) was also part of the silver medal-winning Philippine Team to the 16th Asian Games held in Guangzhou, China where they stunned the highly rated all-Super GM Indian team led by GMs Krishnan Sasikiran (2688) and Pentala Harikrishna (2657) in the semifinals, 2.5-1.5, to advance to the gold medal game versus China.

[31] Antonio (2557) was also part of the Philippine Team that participated in the 3rd Asian Indoor Chess Games held at Hanoi, China in 2009 where he played Board 1.

Antonio eventually ended up in 3rd place after the Buchholz tiebreaks losing out to Epishin, 56–52, but ahead of Villamayor (51.5).

[34] In 2013, Antonio proved that he is still a force to reckon with in chess as he won the 2013 National Rapid Chess Championship held at the Philippine Sports Commission (PSC) National Athletes' Dining Hall, Rizal Memorial Sports Complex, Vito Cruz, Manila.

[37] On November 18, 2017, Antonio placed second in the 27th World Senior Chess Championship 2017 held in Acqui Terme, Italy, in the Open 50+ category behind winner GM Julio Granda Zuniga of Peru.

He won his final round match against Italian IM Spartaco Sarno in 51 moves of a Caro-Kann defense to finish with 8.5 points in a tie with French GM Eric Prie.

He also captured 3rd place in the blitz section with 7.0 points behind winner IM Alexander Reprintsev of Ukraine (8.5) and German Rolf Fritsch (8.0).

[38] On July 21, 2020, Antonio won the 2020 Asian Seniors Chess Championship by scoring 7.5/9 ahead of Uzbek GMs Tair Vahidov, 2nd with 6.5/9, and Alexei Barsov, 3rd with 6.0/9.