The Thai rider quickly made his way through the field, having started from the fifth row of the grid.
A steady charge placed the Thai Honda PTT SAG rider in 15th position with only eight laps left, behind Italian rival Fabrizio Lai.
Wilairot pushed hard in the latter stages of the race to overtake Lai and edge him to 11th place and collect another five points in his World Championship debut season.
After the hard-fought race, the 19-year-old Wilairot, who now has accumulated 16 points from five races, said: "I'm pleased with the way things went. My start was far from perfect but I tried to stay focussed and to regain some ground as quickly as possible.
"As the laps went by, I was improving my lap times gradually and was able to chase the riders in front me. When I caught up with Lai, I knew it wouldn't be possible to open a gap over him. In the last three laps I gave my all and I was able to get my best result of the season. I have to thank my team because, once more, they did a great job."
Team owner Eduardo Perales was also pleased with his rider's performance: "Ratthapark once again proved his potential. He made a great surge from the back and the fight at the end of the race was really impressive. It's a great result. We're in a good position considering we're a private team and our rider has to negotiate a new track for every race. Today, he showed off his talent with a great performance and it's a great boost for the whole team."