The duo fired one-under-par 71s to lead on 136 in the US$1 million event at the Black Mountain Golf Club.
South Korea's Mo Joong-Kyung was third on 137 while Thailand's Chawalit Plaphol carded a 69 to share fourth place on 138.
Hua Hin-born Prom, whose round included bogeys at the first and final holes, said he should have done better.
"I played well although the winds were stronger than the first day," said the 29-year-old, who made five birdies and four bogeys.
"I would have had a better score had I not made mistakes at the last two holes. I will try not to think too much about the title and just to play my game. At this course, several players have a chance to win."
Bidding for his second title on the tour after his success in 2006, Prom said he wanted to win in his hometown for a place on the Asian team in the inaugural EurAsia Cup in March.
With two titles under his belt, Mo believed that he stood a chance to end his six-year title drought after two good rounds.
"I am happy with my performance as the course is so challenging," he said. "Because of the wind, you need to keep the ball flight low."
Four-time Asian Tour winner Chawalit, who won the season-opening Myanmar Open, made four birdies and one bogey.
"It will be good to start the year with a win," he said.
Hua Hin native Prayad Marksaeng and Sweden's Johan Edfors, who won the Black Mountain Masters in 2009, were joint 10th on 139.
Seven-time Asian Tour winner Prayad had an eagle, four birdies and five bogeys.
"It is tough to play in windy conditions," he said.
Amateur Danthai Boonma, the SEA Games gold medallist, hit a 71 for 143 while his SEA Games teammate Poom Saksansin made the cut on 144 following a 74 in his professional debut.
Jazz Janewattananond posted a 72 on 145 alongside 2012 Asian Tour No.1 Thaworn Wiratchant and defending champion Arnond Vongvanij (74).
"My approach shots were quite poor. I did not give myself many chances," said the 18-year-old Jazz, who has regularly practised at the Black Mountain Golf Club.
The cut was made at 146 and 70 players including 22 Thais qualified for the weekend.
Among those who missed the cut included Chinnarat Phadungsil (147), Panuphol Pittayarat (148) and Thanyakorn Krongpha (148).
LEADING SECOND ROUND SCORES
136 - Prom Meesawat (THA) 65-71, Rikard Karlberg (SWE) 65-71
137 - Mo Joong-Kyung (KOR) 69-68
138 - Adam Groom (AUS) 69-69, Kodai Ichihara(JPN) 70-68, Chawalit Plaphol (THA) 69-69, Kieran Pratt (AUS) 68-70, Lin Wen-tang (TWN) 66-72, Pavit Tangkamolprasert (THA) 69-69
139 - Johan Edfors (SWE) 70-69, Prayad Marksaeng (THA) 68-71, Hung Chien-yao (TWN) 72-67, Alex Cejka (GER) 70-69