The former Dortmund star struck in the ninth and 71st minutes with terrific goals to kill the dream for Thistle and give Rangers the chance of a sweet Cup double.
Skipper Barry Ferguson made absolutely certain with a third goal in 77 minutes – only his second from open play this season – and the build-up starts now for a showdown with Celtic which really could be the launchpad for Rangers under McLeish.
Nerlinger had scored twice in three games when his season fell apart seven months ago when he suffered a foot injury which caused him an extraordinary problem, culminating in surgery in the USA over the winter.
He had worked long and hard to get back to full fitness and the evidence of his ability was glaring albeit against First Division opposition which not only augurs well for the remainder of this season but next season’s campaign too.
The Rangers players were keen not to experience the wrath of McLeish at half-time – as they had done a week ago at the same venue – and looked as though they were on course for a simple passage by scoring early.
Nerlinger’s strike after only nine minutes looked to have set the scene for a big Rangers win but a combination of misfortune and misfiring meant that the Jags were still in the game at half-time, just one behind.
And that probably meant that the dressing room pep talk had more spice than it might have done.
Nerlinger was involved as early as the third minute when Jags skipper Danny Lennon slammed into him on the halfway line. Lennon was immediately booked as Nerlinger lay on the turf but the German midfielder did not take long to exact revenge in the best possible way.
It was Andrei Kanchelskis who started the move as he sped down the right and hit a low pass into Tore Andre Flo. The Norwegian striker cleverly stepped away from Lennon and then clipped the ball square for Nerlinger who drove a low left foot shot into the right corner.
The former Bayern and Dortmund star almost scored again from the same position in 31 minutes when Ferguson played him in but this time his shot flew the wrong side of the upright.
And that was one of only three other decent chances Rangers had to extend their lead in the first half which was obviously a source of frustration to McLeish.
Flo is sometimes criticised for his power in the air but he rose well to flick on Ricksen’s cross in 26 minutes and suddenly Caniggia had a clear sight of goal. He tried to place his shot in the left corner but Kenny Arthur made a great save, diving to his right.
Amoruso and Vidmar might have done better with headers from corners while McCann hit the bar direct from a corner in 28 minutes and it all meant that Thistle were still very much in the game.
With Gerry Britton up front there was always a danger that the Jags might get back on level terms but the former Celtic striker never really had a chance.
Still the longer it went at 1-0 the better it was for the Maryhill men and if they had had more bite up front they might have caused Rangers a problem as the Ibrox men struggled to make the game safe.
Flo stumbled in 62 minutes as Kanchelskis delivered a great ball from the fight and then a minute later the former Chelsea man headed straight at Arthur after another good centre from the Russian winger.
Fittingly it was Nerlinger who settled the issue in 71 minutes with a quite superb goal. He took a pass from Ferguson just inside the Thistle half and drove forward with power and purpose.
Cleverly he played the ball wide for Peter Lovenkrands and raced into the box looking for the return. The young Dane delivered with a good ball in and Nerlinger fired a left foot shot into the net.
Skipper Barry Ferguson made absolutely sure that a comeback was beyond Thistle when he scored an excellent third goal in 77 minutes to guarantee an Old Firm Final on May 4.
It was great inter-play as Kanchelskis played the ball forward for Flo who spotted Ferguson’s run into the box and laid the ball into his path.
Ferguson took one touch and then deftly tucked a left foot shot into the right corner and followed it up with a customary punch of the air with his right fist.
It was hardly the most convincing of performances in the sense that Rangers had played a lot better this season, but they got the job done and now the countdown is on for the May 4 showdown with Celtic when Alex McLeish can really make his mark as Rangers boss.
RANGERS: Klos; Ricksen, Malcolm, Amoruso, Vidmar; Kanchelskis, Ferguson (Hughes 80), Nerlinger, McCann; Caniggia (Lovenkrands 66), Flo. Subs not used – McGregor, Dodds, Latapay.
Bookings: Nerlinger (89)
PARTICK THISTLE: Arthur; Kelly, Archibald, Paterson, Craigan, Deas; Walker, Lennon, McCulluoch (McAnespie 78); McLean (Cameron 66), Britton (McKinstry 84). Subs not used – Gow, Dolan.
Bookings: Lennon (3), Cameron (68)
Ref: Mike McCurry.
Man of the match: Christian Nerlinger
Moment of the match: The superb move which led to Nerlinger’s second goal.