Tien, attempting to give 16 and 18 enough time to escape, subsequently uses up all his energy in a vicious attack, and falls to the ground. Goku knows that Cell is far stronger than Tien, so he descends on the battlefield to help Tien recover. Whilst there he notices Piccolo is still alive, but he’s hanging on barely by a thread. Cell desires to fight Goku immediately, but Goku uses his Instant Transmission to get back to Kami’s lookout successfully, and Vegeta and Trunks finally emerge from the Hyperbolic Time Chamber.
Credit to Wikipedia