Robertson, the Caley Thistle manager, sees no reason why his leg-weary side could not have played the last-four ties on Thursday and Sunday, rather than Tuesday and Friday. There was obvious fatigue in both camps yesterday, but Ayr – 3-1 down from the first – were the better side for long spells.
A tremendous opener by young Luke McCowan had home nerves fraying for long enough, before Donaldson – with his first goal of the season – sparked home delight.
Robertson said: “We didn’t want to say anything much before the game but I don’t understand why we cannot play the first leg on Thursday and the second leg on Sunday. It’s ludicrous when you are trying to get the best product on the pitch.
“I don’t think it is fair asking us to play Tuesday/Friday when Dundee United have had nine days’ rest.
“Until the goal we looked nervous. It’s a strange situation. No matter how much you tell them, psychologically with a two-goal lead you don’t know whether to stick or twist. We told them to go and play a normal game but Ayr’s goal woke us up a bit.
“At 1-0 with 20 minutes to go you could see a goal coming but you didn’t know whether it was us or Ayr. Thankfully we got it.”
Nerves were evident in a tight opening spell, before Ayr’s top scorer Lawrence Shankland raced behind the home defence after 16 minutes only to be shut down by Jamie McCart.
The hosts thundered back with a superb Liam Polworth run and through pass forcing Ayr keeper Ross Doohan to save at Jordan White’s feet.
A minute later, Ayr grabbed the opening goal. Shankland fired a long ball wide to Declan McDaid on the right and, with defenders streaming back, the winger did well to pick out 19-year-old McCowan for a six-yard rocket into the roof of the net.
The hosts struggled to find fluency or create chances in retaliation and lost winger Tom Walsh to a hamstring problem early in the second half.
Ayr spurned a great chance after 72 minutes as substitute Michael Moffat carved space for Robbie Crawford, but saw his team-mate curl a 20-yard attempt only just high and wide.
The hosts mustered a vital equaliser just inside 80 minutes. After a foul on Aaron Doran out wide, Liam Polworth’s dipping delivery found defender Donaldson rising to skim his head on the ball with a perfect contact to beat Doohan from six yards.
It had been a fine effort by Ayr, League One winners last year, and home manager John Robertson waited to applaud them off the field.
Ayr manager Ian McCall said: “I’m very proud – very proud of the last two years. There are a lot of boys out there who will be leaving and they didn’t leave anything in the dressing room. I thought we were the better team over both legs, the better footballing side, but I congratulate Caley Thistle and wish them well because it was a cup tie and it’s about winning.”