The two sides played out a hugely entertaining 2-2 draw in Upper Coll which leaves the tie delicately poised for another barnstorming 90-minutes.
Gordy Maciver opened the scoring for Lochs in the first-half before Chris Stone fired home from distance to level.
Stephen Kettings edged the Blues in front for a spell in the second until Jim O’Donnell, Lewis and Harris football’s top scorer in 2016, notched another to make it 2-2.
After the match David Macmillan said he was pleased with the result which ensures it will be a case of winner-takes-all in Lochs next week.
“It was a bit scrappy although the pitch didn’t help as it was heavy and quite boggy,” he said.
“But both teams played football as much as we could. We are pretty happy with 2-2. Back had a lot of pressure but they didn’t create many clear cut chances.
“They were certainly the better team for the latter part of the first-half and a good period in the second-half. We are happy to go to Lochs with a 2-2.”
The game had been in doubt earlier in the day but it dried out relatively quickly throughout the afternoon for the clash of the two island football heavyweights.
As Eilean an Fhraoich tradition dicates, all players not eligible either through birth, residence or parentage in the respective distrcits were unavailable for each side while they were able to ‘call up’ players from other club teams who qualify under the rules.
Back drafted in Kettings from Point and Chris Mackay from Lochs while Lochs took Gordy Maciver and Allan Farrell from Back and Connor Maciver, Ross Allison and Ali Morrison from Athletic.
The visitors took the lead after a clever turn from Craig Maclean left Craig Macleod bamboozled with the Lochs man spinning in behind and forcing a stop from Michael Maciver.
The Back man could only parry the shot into the six-yard box where Maciver had gambled and was unchallenged as he rolled the ball into the net from close range.
Back cranked up the pressure in the latter part of the half but they found Donald ‘Nomie’ Macdonald and Graeme Mackenzie in stubborn mood in the Lochs defence.
They were limiting the Blues to efforts from distance and coping relatively comfortably until the stroke of half-time when Stone pulled one out of the top drawer.
The Back number eight was one of his side’s top performers on the night with his positive running and willingness to demand the ball from his team mates at every opportunity and sent a shot from 25-yard sailing over Gordon Mackenzie into the net.
Back continues to set the pace after the restart and Kettings had the Back defence on their feet when he rose to meet a cross into the box only to head wide.
Kettings, playing up front for Back on the night, made amends shortly afterwards with a shot from the edge of the box which skipped off the wet turf and nestled inside the post.
In keeping with the trend of the match there was another twist to come as the pendulum swing back in the Maroons’ favour. A series of positive moves forward, aided by sub Connor Maciver’s willingness to gallop after every ball forward and harass the Back defence into mistakes with no time on the ball, brought them level.
This time the goalscorer was O’Donnell who raced through the centre of the defence, winning a footrace with Maciver who charged off his line before toeing the ball under the keeper and in the net.