#1: Scott McDonald can be a midfield star
Despite admitting in the build up to the new season that he is still adjusting to his new position, Scott McDonald looked at home at the tip of Millwall's midfield.
In many ways it's no surprise given that the Australian's best attributes are his close control and direct running style, but he exceeded expectations with his performance against Leeds.
At times McDonald needed to release a pass earlier than he did, but his ability to drop a shoulder and jink past a defender created countless attacking situations.
With time, he'll only get better in what are still slightly alien surroundings for the striker.
Having struggled for form in his first season with the club, McDonald says he intends to seize a "fresh start" with both hands in 2014-15.
And on Saturday's showing, you wouldn't bet against the 30-year-old featuring much more prominently for the Lions over the coming months.
#2: Alan Dunne has picked up from where he left off
48 hours after being confirmed as Millwall's new captain, Alan Dunne led by example at the heart of defence.
And his resolute display represented a continuation of his fine form from the end of last season.
Dunne has not put a foot wrong since being converted to a centre back and he deserves huge credit for establishing himself as a key figure in Ian Holloway's plans for the future.
On Saturday, the 31-year-old made a vital goal-line clearance at 1-0 to keep out Noel Hunt's shot and prevent Leeds from gaining the upper hand.
And his calmness under pressure got the Lions out of several tight spots: facing his own goal, Dunne's back passes to David Forde were flawless.
But Dunne was no-nonsense when he needed to be – and could even have scored with a first-half header. A fantastic all-round display.
His partnership with Mark Beevers continues to bode well.
#3: 4-1-4-1 and long diagonal passes
Holloway has had a full pre-season to work on Millwall's tactics and structure, and he's clearly made the most of that time.
Millwall weren't at their flowing best and faded slightly in the second half but they were an effective and well-organised unit throughout.
The Lions lined up in a 4-1-4-1 formation which shifted to 4-3-3 when they were on the attack. In this system, Shaun Williams and the two full backs have crucial roles to play.
When Holloway's side had the ball in their own half, Williams would drop deep, almost to become a third centre back, to keep possession ticking over.
The approach was patient – but after drawing Leeds onto them, Millwall hit quick diagonal passes to the opposite flank to create space and launch attacks.
Full backs Scott Malone and Carlos Edwards were pinging cross-field passes to each other all afternoon – and Williams was always willing to receive the ball and switch the play.
It's a smart, fluid system – and will become more polished with practice.
#4: Lee Martin ran himself into the ground
Lee Martin took defending from the front to a new level with his performance.
Martin was closing down the Leeds back four at every opportunity, forcing mistakes and winning the ball back high up the field.
After the game, visiting manager David Hockaday compared his side to rabbits in the headlights and admitted they had panicked in response to Millwall's pressing game.
Martyn Woolford was equally hard-working on the opposite flank and helped to pen the Whites inside their own half.
#5: Worst Leeds side at The Den in years
As good as Millwall were, Leeds were really, really bad.
They were passing sideways for the whole of the first half and it didn't take long for the first boos to ring out from the 2,000 fans in the away end.
Their three-man midfield of Luke Murphy, Rodolph Austin and Michael Tonge was non-existent and striker Souleymane Doukara barely troubled the back four.
Leeds improved once Matt Smith came on – you could see why Holloway remains keen on signing the big striker, who was given little to no service up front.
But overall, the visitors were woeful and it's hard to see Hockaday lasting the season.