Brendan Rodgers was looking to guide the Swans into the top two of England's second tier for the first time since the club's glory days of the early 1980s, and all was going to plan when full-back Angel Rangel rose unmarked to head home Andrea Orlandi's corner in the 18th minute.
The Spaniard had failed to find the net in over 18 months but now has two goals in four games, yet it was not enough to take all the points as Tamika Mkandawire soon drilled home a leveller for the Lions after the ball broke his way on the edge of the area following a goalmouth scramble.
It was a fair result on the overall balance of play after what was an entertaining first hour but rather low-key final 30 minutes, with Wales international Steve Morison wasting two gilt-edged chances to win it for the visitors late on.
Influential skipper Garry Monk returned to the heart of Swansea's back line having missed the last three games with a calf injury.
Millwall boss Kenny Jackett, who guided the Swans to promotion during a successful spell in charge of the club between 2004 and 2007, also made just the one switch, striker Josh McQuoid coming in for his full debut after his arrival from Bournemouth.
And it was the visitors who threatened with less than 60 seconds on the clock, forcing Dorus de Vries to get down smartly.
It signalled a busy opening 15 minutes which saw Scott Barron fire over and Scott Sinclair twice go close for the hosts at the other end, with Lions captain Paul Robinson also limping off.
It was no surprise when the deadlock was broken after 18 minutes, Rangel ensuring the breakthrough went City's way when he capitalised on some slack defending to head home unmarked from Orlandi's outswinging set-piece.
If Jackett was fuming with his side's defensive lapse then it was counterpart Rodgers' turn to feel aggrieved eight minutes later.
Swansea's rearguard repeatedly failed to clear their lines after a jinking run from Jason Puncheon, eventually allowing Mkandawire to convert.
Chances continued to open up, Nathan Dyer taking Mark Gower's superb pass into his stride before being denied by David Forde.
Swansea started to dominate proceedings as the half wore on, keeping possession within their ever-present passing style, and Dyer wasted a great chance to hand the hosts the lead in injury time when he blazed over from close range.
Much like the first half, Millwall started the second on the front foot with McQuoid failing to hit the target with a headed opportunity.
De Vries was then called upon to produce a great save to tip away McQuoid's header from James Henry's free-kick.
The second half continued to pass by in the same fashion as the first with openings coming at either end, and Rodgers introduced loan debutant Jermaine Easter in the 56th minute in the hope of taking advantage.
But the clash then lost its way over the subsequent 35 minutes, with very little to stir the 13,853 present.
Yet Morison had two chances in the final four minutes to make all that irrelevant for Millwall, however he could only fire horribly wide before being denied by De Vries when in great positions.