Juan Martín del Potro is making a late run to qualify as one of the chosen eight for next month's ATP Tour Finals in London after his determined fight-back to beat Alexander Zverev at the Shanghai Rolex Masters.
Aljaz Bedene lasted just 12 minutes against Alexander Zverev at the Shanghai Masters before retiring for the second time in two weeks.
Federer is hot on the heels of world No. 1 Rafael Nadal as he looks to close the gap at the top of the ATP rankings and he will perhaps hope to avoid another tough meeting with the 2009 US Open champion.
The 46th-ranked Harrison led 4-2 in the third set and then 6-3 in the tiebreaker. But 16th seeded Del Potro found his form in the second set, scored 5 love games and levelled the set-score with a 7-5 victory in the tie-break.
A fan at least came away with a demolished racquet after Zverev handed it to a spectator.
Earlier on Thursday, Grigor Dimitrov booked his place in the quarter-finals, downing Sam Querrey 6-3 7-6 (7-3). Im a bit pissed off because I feel like I played well and thats the upsetting part of it I could have done great in this tournament..
In other third-round action, Spain's Albert Ramos Vinolas stopped German Jan-Lennard Struff 7-6 (7-4) 6-4.