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Welling maintained their place in non-league's top flight for a third season despite losing on Saturday.
The Wings knew that they only had to match Alfreton's result at Bristol Rovers to retain their Vanarama Conference status.
So with Alfreton losing 3-0 at half-time the second half at Park View Road was largely academic after an entertaining, if goalless, first half.
Alfreton went on to lose 7-0 while Welling were beaten by Steven Hewitt's 30-yard wondergoal, which was worthy of winning any contest.
That said, the first half saw Welling dominate and create a series of chances. Home wins earlier this month against Wrexham and Kidderminster provided the foundation for Welling's survival but they actually had more opportunities against Southport than in those matches.
Dominic Vose waltzed along the byline but saw his right-foot drive whistle just past the upright before Sam Berry headed over and Ross Lafayette shot wide.
Keeper Tony Thompson then punched captain Jake Gallagher's cross only as far as Vose, who rounded Thompson but saw his shot deflected off the line and onto the post by the covering Luke Foster.
Foster then headed narrowly wide at the other end and Richard Brodie's deflected effort caused recalled keeper Jon Henly to worry after an uncomfortable bounce in front of him.
After the break, Kieron St.Aimie somehow failed to connect with Ben Jefford's pinpoint cross from close range while both Vose and St.Aimie shot over as the pace came out of the contest.
Welling replaced Gallagher and Lafayette, the latter in particular receiving an excellent ovation after a successful loan spell form Luton which helped his former club avoid relegation.
The only goal arrived on 78 minutes when Hewitt let fly from 30 yards and saw his strike hit the underside of the bar and bounce over the line.
Tom Davies nearly turned in Jefford's cross as Welling pressed for an equaliser. Proof it wasn't going to be Welling's day came even later when Vose's cross was sliced against the bar by a Southport defender.
But the 1,015 crowd cared little by that stage as Welling's 2-2 draw at Alfreton last weekend proved decisive and they stayed up to complete the great escape.
Welling: Henly, Gallagher (Fagan 60mins), Bush, Vose, St.Aimie, Lafayette (Penny 71mins), Jefford, Berry (Healy 82mins), Corne, Williams, Chambers. Subs not used: McEntegart, Taylor. Attendance: 1,015.