With Forren making his first appearance at any level since signing for the Club in January, the Norwegian's volley on the half-hour had put his side in the ascendancy.
But Liverpool – beaten just twice all season – equalised through Krisztian Adorjan 13 minutes from time to take a share of the spoils.
U21 Coach Martin Hunter made one change to the side that beat West Bromwich Albion a week ago, bringing in Forren for his first appearance since signing for the Club in mid-January.
Paulo Gazzaniga started in goal for the fourth game in a row, while Forren was joined in defence by Calum Chambers, skipper Jack Stephens and Matt Targett.
Despite having made a substitute appearance for the First Team on Saturday, James Ward-Prowse was included in midfield along with Andy Robinson and Corby Moore.
Saints' three-man forward line consisted of Alberto Seidi, Jake Sinclair and Omar Rowe, all of whom have netted in recent weeks for Hunter's side.
Liverpool, meanwhile, selected an XI including four players who have appeared for their first team this season in the form of Andre Wisdom, Conor Coady, Suso and England international Jonjo Shelvey.
It took until the 12th minute for either side to register an effort on goal, and it was Spaniard Suso who tried his luck only to see his 20-yarder easily held by Gazzaniga.
With the visitors in the ascendancy, it was then the turn of winger Adam Morgan to take aim having exchanged passes with Suso but his effort flew well wide.
Saints had the ball in the back of the net on 17 minutes when Rowe's low centre from the left was poked in by Seidi only for the Portuguese winger to see his finish ruled out by an offside flag.
Two minutes later, Rowe was again the provider as his inswinging corner found the head of Chambers but the Southampton right-back headed against the near post from close range.
Forren almost grabbed himself an unlikely goal midway through the first period when he burst over halfway and exchanged passes with Rowe before seeing his vicious drive deflect narrowly wide of Peter Gulasci's goal.
Moments later a superbly-weighted pass out of the Reds' midfield set Morgan clear of Forren but, with only Gazzaniga to beat, the 18-year-old somehow slid the ball wide of the post.
But it was FORREN who scored the game's opener on the half-hour when another good corner by Rowe was not dealt with, allowing the Norwegian to power in from a tight angle.
Defender Forren tried his luck again five minutes later when Robinson's corner was partially cleared, but his first-time volley dipped just the wrong side of Gulasci's crossbar.
Liverpool thought they had levelled three minutes before the break when Shelvey's shot was diverted in by Adorjan but the Hungarian was correctly flagged as being offside in doing so.
HALF TIME: SAINTS U21S 1-0 LIVERPOOL U21S
The first chance of the second half went Saints' way as midfielder Robinson took aim with a free-kick 25 yards out, and his swirling effort had Gulasci back-peddling but dropped just wide of the far post.
Hunter looked to refresh his side's attacking efforts eight minutes into the second half, bringing on Sam McQueen for Seidi on the right flank.
18-year-old McQueen had the ball in the net within two minutes of coming on as he bundled in Sinclair's low cross only to see his effort chalked off by an offside flag.
Then, a few minutes later, more good wing play by Sinclair saw him find onrushing midfielder Moore but his close-range attempt span agonisingly wide of the far post.
Liverpool began to find their feet around the hour mark, with Adorjan seeing one effort saved by Gazzaniga then another excellently blocked by Forren.
The lively McQueen then tested Gulasci after cutting onto his left foot and sending a rasping drive towards the Liverpool goal, before Joao Teixeira saw a powerful shot held by Gazzaniga.
Some great teamwork involving Rowe, Sinclair and Ward-Prowse then saw the ball break nicely for the latter but his piledriver deflected just wide of the visitors' goal.
Moore was then denied from close range by Gulasci while, at the other end, a smart free kick from Suso teed up Shelvey to fire the ball well over the bar and into the empty Northam Stand.
But the visitors did eventually get themselves back on level terms with 77 minutes gone when ADORJAN was picked out by Shelvey's excellent cross, allowing the Hungarian to head in with ease.
Liverpool substitute Jack Dunn then tried his luck with a left-footed snapshot that Gazzaniga held gratefully, before Hunter gave Gboly Ariyibi his Under-21s debut on 90 minutes.
There was still time for one last chance as the impressive Suso jinked his way into the Saints box only to be denied by the legs of Gazzaniga.
FULL TIME: SAINTS U21S 1-1 LIVERPOOL U21S
Saints U21s: Gazzaniga, Chambers, Stephens (c), Forren, Targett, Robinson, Ward-Prowse, Moore, Seidi (McQueen 53), Sinclair (Ariyibi 90), Rowe. Subs (not used): Johns (GK), Curtis, Turnbull.
Goals: Forren (30)
Bookings: Sinclair (65)
Liverpool U21s: Gulacsi, Roddan, Wisdom, Sama, Jones, Coady (c), Morgan (Dunn 73), Teixeira, Shelvey, Suso, Adorjan. Subs (not used): Ward (GK), Nacho, Brannagan, Baio.
Goals: Adorjan (77)
Bookings: Shelvey (44)
Referee: Tim Wood