Defending champions Turnhouse face a team bidding to land the title for the first time in this weekend’s Edinburgh Summer League semi-finals.
But Mortonhall are worthy contenders as this season’s event reaches the business end, having recorded a superb away win over Royal Burgess in the quarter-finals.
Longniddry stages the Turnhouse v Mortonhall last-four tie on Sunday, when Musselburgh take on Baberton in the other semi-final at Silverknowes.
Turnhouse are the title favourites but Moray Hanson will be warning his side not to take Mortonhall for granted after their 5.5-3.5 win over Royal Burgess, winners seven times in the previous nine years.
The visitors got off to a good start with Rob Paterson and Graeme Clark in command of their games throughout.
Ian Dickson then birdied the last for a hard-fought victory before Martin Fitheridge was always down against an on-form Malcolm Pennycott.
Bill Buchan then hit a wonderful second to ten feet at the par-5 sixteenth for a 3&2 victory to give Mortonhall a 4-1 lead before the fun started.
Greg Nicolson put a 2-iron on the last green for a winning birdie to make his game all square. With the last three games on the course all level, Mortonhall weren’t over the line yet but they were when Nicolson won at the second extra hole with a birdie.
“It was always going to be a tough job against Royal Burgess on their own patch,” said Mortonhall team manager Graeme Stark.
“As is usual these days, it’s availability of the ‘top’ players that hinders us most years but, on this occasion, I was able to field a strong squad who obviously played very well to bring about such a result. It will need to be some of the same on Sunday to beat the holders.”
Turnhouse stayed on course for a successful defence of the title they claimed for the first time 12 months ago with a 7-2 home win over Murrayfield.
“We are delighted to have made the semi-final for the third year in a row after coming through an even tougher group this year,” said Hanson.
“We finished in the top position of our group which gave us the home tie against a very good young and talented Murrayfield team who will certainly be contenders for many years to come in the future.
“Again we have had a very experienced squad to call upon and I am also delighted that some of our younger players had the chance to play in a few of the matches and contributed towards keeping our unbeaten record in place.
“The team and the club members are looking forward to our semi-final at Longniddry against Mortonhall. We know that Mortonhall are a very good team and I am sure it will be a well- contested close match.”
Musselburgh, who made home advantage count to beat Longniddry, the 2016 beaten finalists, last claimed the title exactly 40 years ago, having also triumphed in 1974 and 1975.
“We are relishing the opportunity to achieve this feat again and I’m really proud of the boys for making it through to the semi-final,” said Musselburgh team manager Calum Burgess.
“We have had a brilliant campaign so far, winning more matches than any other team with nine out of 11 matches and knocking out Longniddry will give us the confidence to prove we can go all the way this year.”
Baberton, bidding to come out on top for the first time since 1999, completed the last-four line-up with a dramatic victory over 2014 champions Bruntsfield Links.
It finished 4.5-4.5 at Juniper Green, with Dougie Waugh emerging as the Baberton hero as he won at the 20th against two-time Lothians champion Alan Anderson.