McLean's eight-under total matched that of Walker Cup youngster and playing partner Stiggy Hodgson (Sunningdale) as they finished five shots behind the winner, Matthew Southgate (Thorpe Hall) of Essex.
"That's my best in five attempts at this tournament," said McLean, Edward Trophy winner earlier in the season.
"I was hitting the ball pretty straight and, looking back, I could have finished second on my own but for a double bogey 6 with a lost ball at the second in the final round. That spurred me on to birdie the third, fourth, fifth, tenth, 12th, 13th, 16th and 18th.
"I knew it was between me and Stiggy for second place and when he holed from about 20ft for a birdie at the last I knew I had to follow him in from seven feet, also for a birdie, which I did. So that was a nice way to end."
Southgate, 21, has yet to gain a full England cap, his biggest win prior to this being in his home county, at the Essex open amateur championship."I couldn't have picked a better place for my biggest win," said Southgate who shared the lead at halfway with Denmark's Daniel Lokke and Ben Westgate (Trevose) on six-under-par 138.
Hodgson had taken the lead after a third-round 67 for 207, a one-shot lead over Southgate who forged clear on his own to win by five shots with a closing 67 (34-33) for a 13-under-par total of 275.
Second Scot was Michael Stewart from Troon Welbeck, who finished joint seventh on 282 with Sunday rounds of 72 and 69.
Stirling University student James White (Lundin) shared 15th place on 284, closing with 70 and 71, while Matthew Clark (Kilmacolm) finished joint 24th on 286 with rounds yesterday of 67 and 75.
Murrayshall's Gavin Dear won 795 for a joint 20th finish in the Alps Tour event, the Open International d'Ile de France at Golf de Disneyland yesterday. Dear had four consistent rounds of 70, 69, 69 and 71 for a five-under-par total of 279. He finished 13 shots behind first-time winner Italian Nunzio Daniele Lombardi who won the 7,250 with four shots to spare with an 18-under-par total of 266.
Lothians won the Scottish boys' area team golf championship for a record ninth time at Peebles Golf Club yesterday.
Grant Forrest, Anthony Blaney, Graeme Duncan and Fraser Thain totalled 356 in the foursomes-singles format. They finished four shots ahead of Lanarkshire and South, with Lanarkshire placed second by virtue of having the best fourth individual score.