 Yeon Namsaeng sent his son (later known as Cheon Heonseong/Quan Xiancheng (), as Yeon () was the same character as Emperor Gaozong's grandfather Emperor Gaozu's name Yuan and therefore could not be used as part of naming taboo) to seek aid from Tang.When Emperor Gaozong sent the generals Pang Tongshan () and Gao Kan () to aid Yeon Namsaeng, Yeon Namgeon tried to intercept them, and Xue, who trailed them, marched forward to aid them, allowing them to defeat Goguryeo forces together.After they captured the cities of Namso (, in modern Tieling, Liaoning), Mokjeo (, in modern Fushun), and Changam (, in modern Benxi, Liaoning), they were able to rendezvous with Yeon Namsaeng.