BEIJING -- REIGNING ASIAN ARCHERY champion Mark Javier battled through the effects of diarrhea all afternoon and wound up 36th in the ranking round of the men’s individual Fita 70-meter competition Saturday at the 29th Olympiad here.

Marksman Eric Ang virtually shot himself in the foot, however, with a dismal opening string and looked spent going into the second day of the trap competition at the Beijing Shooting Range.

The 100-lb Javier surged back with 333 points in the second 36-arrow half to pool 654 at the Beijing Green Archery Field and set up a knockout duel with Chinese Taipei’s Kuo Cheng-wei in one of 32 head-to-head matches on Wednesday.

Javier and Ang were the first of the 15 Filipinos to see action here Saturday, the Games’ first day of competition.

Kuo, a 25-year-old former World Cup runner-up, ranked 29th on scores of 323 and 336 for 659.

Mexico’s Juan Rene Serrano put the vaunted world champions from South Korea to the shade with a sparkling 679 points, including 12 bull’s-eyes, two more than Javier’s.

The Mexican from Guadalajara, the 2007 World Cup runner-up, bested India’s Mangal Singh Champia and Ukraine’s Viktor Ruban by one.

Bum stomach

‘‘Mark woke up in the morning clutching his stomach,” said Javier’s coach, Jennifer Chan. ‘‘The diarrhea was gone, though, when we boarded our vehicle for the venue. I don’t know how he managed to get back his bearing in the afternoon, but he did.”

Right off the first few buck shots, however, it was apparent trap-shooter Ang was fighting for survival.

At 5 feet 5 easily the shortest among the 35 trap-shooters in the range, Ang managed just 65 birds out of a perfect 75, his hopes of advancing into the finals shootoff getting undone by a tragic 19 in the first 25-clay string at the trap venue north of the smog-choked city center.

Although the 37-year-old businessman from Laoag City got himself back on target with a 24 in the next set, he all but bombed out of the competition with a 22 in the competition’s third of five strings.

With just 50 birds to go on Sunday, Ang lay eight points off the two co-leaders in a tie for 29th place with China’s Li Yajun, American Bret Erickson, New Zealand’s Graeme Ede and France’s Stephane Clamens.

Leaders

Only two other shooters scored worse than the Filipino’s group.

Italian world record-holder Giovanni Pellielo and the Czech Republic’s David Kostelecky led the field with 73s, with Italy’s Erminio Frasca, Russia’s Alexey Alipov, Slovakia’s Erik Varga, Australian world champion Michael Diamond and Croatia’s Josip Glasnovic one bird off the pace.

Only the top six scorers after 125 birds will move into the finals shootoff.

And the prognosis is already bad for Ang, the country’s lone shooting entry.

At the 2007 World Cup in Suhl, Germany, he shot an amazing 121 birds but lost in a shootoff for the sixth finals spot to Alipov, the Athens Olympics gold medalist. Even if Ang shoots a perfect 50 in the last two strings, he will only score 115, usually not enough in such a world competition to land him in the magic six, according to Philippine delegation officials.

‘‘The first string was crucial, it shouldn’t have been that bad,” Philippine National Shooting Association president Art Macapagal quoted Ang’s coach, James Chua, as saying. ‘‘Eric could not get into a rhythm right away.”

A win for Javier over Kuo in the round-of-32 will set him up against the winner between Brazil’s Luiz Gustavo Trainini and South Korea’s Park Kyung-mo, also on Wednesday.

Resilient

‘‘He’s very focused now, I hope he gets past Kuo,” said Chan of Javier, the Bachelor of Science graduate from Silliman University in Dumaguete City.

Philippine Sports Commission chair William “Butch” Ramirez said Javier showed his resilience by not being slowed down by diarrhea.

‘‘Javier’s training molded his fighting spirit,” said the head of the government sports agency. ‘‘He already showed that in last year’s Asian championships.”