Sieb Dykstra kept shaky Dundee United in the Tennents Scottish Cup at Somerset Park with an outstanding display.

The big Dutchman proved unbeatable as the First Division side almost pulled off a shock result.

Dykstra saved a penalty with five minutes to go, reading it right as Andy Walker drove the ball in.

He pushed the ball onto the bar as Ayr manager Gordon Dalziel turned his back and hid his eyes, unable to watch.

It was a crucial miss for Walker and now the teams will replay at Tannadice on Tuesday for the right to meet Celtic in the semi-finals next month.

United are making hard work of their cup campaign and this is the third time in succession they have been taken to replays by clubs in divisions below them.

Queens Park and Clydebank also made them struggle as did Ayr today in front of a bumper crowd.

United badly missed the experience of veteran defender Maurice Malpas who was sidelined with a hamstring injury.

Ayr were busy and inventive and certainly shaded in the first half with Gary Teale and Andy Walker prominent as they put the Premier League side under pressure.

Teale delivered a fine cross from the left after 17 minutes and Glynn Hurst's header seemed bound for the net. But somehow Dykstra got across his goal to push the ball away.

The United keeper then stood up eight minutes later when Teale tried to curl the ball past him and took it safely.

United struggled to get going in the first half and their only effort of note came from striker Billy Dodds whose shot with the outside of his right boot went narrowly over the top.

Ayr continued to look menacing and almost took the lead two minutes into the second half when Walker thumped the ball in from 20 yards only for Dykstra to push it away.

That seemed to spark United into action and Ayr defender David Craig got back quickly to divert to safety a shot from Dodds after keeper David Castilla had been beaten.

Then the French keeper tipped away a 25-yard shot from Jim Paterson and a header from Jason de Vos went inches wide following a cross from Joe Miller.

Ayr continued to threaten and Hurst was narrowly wide with a shot after Davis had put him clear.

Then came that penalty miss from Walker, minutes after Dykstra had again made a superb block.

The penalty was awarded after Andy Millen was bowled over by Tommy Mols but the home crowd were left frustrated.

United almost sealed victory at the death but Castilla managed to save cleanly from first Kjell Olofsson and then Dodds as the game finished with plenty of excitement.

Teams:

Ayr: Castilla, Robertson, Barrick, Millen, Traynor, Craig, Hurst, Davies (Ferguson 83), Walker, Teale, Lyons.

Subs Not Used: Reynolds, Nelson.

Dundee Utd: Dykstra, Patterson, Paterson (Skoldmark 75), Mols, De Vos, Duffy, Miller (McLaren 77), Eustace, Olofsson (Mathie 90), Dodds, Easton.

Booked: Patterson, De Vos, Eustace, Duffy.

Att: 5,508

Ref: S Dougal (Glasgow).