Milkins will face Jiahui, following the youngster's impressive win over Shaun Murphy.
Meanwhile, Selby, who beat Matthew Selt, will take on Gary Wilson in the next round.
All of today's matches at the Crucible:
Robert Milkins 10-9 Joe Perry
Perry raced to a 5-0 lead before Milkins was able to settle. The duo traded frames until the score-line hit 8-4 to Perry's advantage.
That was until Milkins began to pull away, as he then took all but one frame from the next seven to win 10-9.
Mark Selby 10-8 Matthew Selt
Selby started brightly, claiming the first three frames for a 3-0 lead before Selt hit back with two of his own.
But 'the Jester' proved to have more in the tank as he extended his lead to 6-2 after the eighth frame. It was a fairly well-fought affair until the end, with Selby taking four of the last nine to win 10-8.
Shaun Murphy 9-10 Si Jiahui
Murphy started positively and moved comfortably into a 3-1 lead after the first four frames.
But it didn't take Jiahui too long to give the world No. 4 something to worry about, as he raced into the lead at 5-3, which would then be extended to 9-6.
Murphy may have thought he had momentum on his side after he clawed the score-line back to 9-9, but his young opponent claimed the final frame for the win.
