5 teams (Thistle, Third Lanark, Hearts, QP and Rangers) entered the FA Cup in 1885/86. The SFA warned them all that if they were drawn against a professional club and played the match they would be expelled from the association. There was no problem for Thistle because they were drawn against Queen's Park. They lost 1-5.
Thistle got to the 5th round the following season. The Cliftonville match must surely be the only time in history of the FA Cup that a Scottish club has been drawn against an Irish club. After beating Cliftonville 11-1 they lost 0-1 away to Old Westminsters. Here's a potted report of the match...
On 29/1/1887 Thistle's final attempt to lift the FA Cup ended in defeat at the Oval against Old Westminsters who won 1-0. "Sporting Life" reported that Thistle played "a good, honest and withal an exceedingly fair game. The match was indeed a most pleasant one throughout and the Thistle left a most favourable impression on metropolitan footballers". So Thistle left with some credit. It was less so for the home crowd. "Their own impression of the London crowd can hardly have been gratifying, as the spectators were most undemonstrative except in the case of any piece of good play by one of the Old Westminster team". Perhaps the shock of seeing a bunch of players made up of shipyard workers and the like was too much for the fans of the club linked to one of England's oldest public schools and who (ironically) had been an influential voice in the development of football and the laws of the game in England 20 years earlier. For their troubles, Thistle received £21.15s.6d. gate money. "The Sportsman" reported that the Thistle party would be arriving in the capital at 4am on the day of the match. They, too, deplored the "unwarrantable amount of partisanship" on the part of the spectators.