You’ve swum 3.8km.
You’ve ridden 180km.
You get through T2, put your running shoes on, and finally start the marathon.
And something surprising happens.
You feel pretty good.
Your legs are turning over. The crowds are cheering. You’re finally running rather than sitting on a bike.
Your planned pace feels easy.
So you speed up.
That’s exactly where an Ironman marathon can begin to unravel.
One of the most important pieces of advice I can give you for the Ironman run is simple:
Respect the first 10km.
The First 10km Can Lie to You
Running off the bike feels different.
Initially, your perception of pace can be distorted. After spending hours cycling, the change in movement can make your running stride feel surprisingly quick and energetic.
Add race-day adrenaline, spectators, other competitors, and the excitement of finally starting the marathon, and it’s very easy to run faster than planned.
The dangerous part?
It might still feel easy.
That’s why you need discipline.
Don’t judge your Ironman marathon pace solely by how good you feel during those opening kilometres.
You’ve still got a very long way to go.
You’re Not Starting a Marathon Fresh
This sounds obvious, but it’s worth reminding yourself.
You’re not standing on the start line of a standalone marathon after a taper and warm-up.
You’ve already completed a 3.8km swim and ridden 180km.
Your body has been working for hours.
You’ve used energy.
You’ve accumulated muscular fatigue.
You’ve been fuelling and hydrating all day.
And now you’re asking your body to run 42.2km.
That means your Ironman marathon needs to be paced differently from the marathon you might run when fresh.
Let People Run Past You
Just like on the bike, one of the hardest things to do early in the Ironman marathon is let other athletes go.
Someone runs past.
Then someone else.
Their pace looks comfortable.
You think:
“I can run with them.”
Maybe you can.
For 5km.
Maybe even 10km.
But can you run with them at 30km?
That’s the question that matters.
You don’t know how strong a runner they are, how well they’ve paced the bike, or whether they’re about to make a very expensive mistake.
Let them go.
Run your race.
There’s plenty of marathon left to see them again.
The First 10km Should Feel Controlled
I don’t want you shuffling unnecessarily slowly.
But I do want the opening section to feel controlled.
Your breathing should be settled.
Your running should feel smooth.
Your intensity should feel sustainable.
You shouldn’t feel as though you’re already racing the marathon.
If you’re thinking:
“This feels almost too easy.”
Good.
That’s far better than reaching 8km and wondering whether you can maintain your current effort for another 34km.
Don’t Try to Bank Time
One of the most dangerous endurance racing ideas is trying to bank time.
You feel good, so you run faster than planned.
Maybe you’re targeting a particular finish time and decide that getting a few minutes ahead of schedule gives you some breathing room later.
Unfortunately, your body doesn’t work like a bank account.
Those faster kilometres aren’t free.
You’re increasing the physiological cost of running at exactly the stage of the marathon when patience matters most.
You might gain two minutes during the opening 10km.
But if that contributes to walking later, you could lose those two minutes many times over.
Don’t bank time. Bank energy.
Use the First 10km to Settle Into the Run
Think of the opening 10km as your transition into the marathon rather than the beginning of an immediate race against the clock.
Get your running legs underneath you.
Relax your shoulders.
Settle your breathing.
Find a comfortable rhythm.
Continue your fuelling and hydration strategy.
If you’re strategically walking aid stations, begin doing it now rather than waiting until you’re exhausted.
Everything should be about creating a rhythm that you can continue.
The marathon doesn’t need to feel difficult yet.
It will take care of that later.
Your Pace May Need to Change With Conditions
Don’t become obsessed with holding one exact pace regardless of what the course gives you.
Heat matters.
Wind matters.
Hills matter.
Your condition coming off the bike matters.
If your planned pace suddenly requires significantly more effort than expected, forcing the pace simply because it’s written on your race plan can be a mistake.
Respond to the conditions.
Your goal is to control your effort, not blindly chase a number on your watch.
Keep Fuelling
The marathon isn’t the time to forget everything you’ve practised with your nutrition.
You may have been racing for many hours by this stage, and eating or drinking might be becoming less appealing.
But you’ve still got a marathon to complete.
Stick with the fuelling strategy you’ve practised.
Use the aid stations deliberately.
Drink.
Take your planned nutrition.
Cool yourself when required.
Then keep moving.
The decisions you make during the first 10km aren’t just about pace.
They’re about setting up the remaining 32.2km.
Break the Marathon Down
Don’t leave T2 thinking:
“I’ve got 42.2km to run.”
That can feel enormous.
Your first job is simply to get through the opening 10km under control.
Then reassess.
How are your legs?
How is your stomach?
How is your breathing?
Are you maintaining your planned effort?
Are you fuelling?
From there, move onto the next section.
You don’t need to race the entire marathon at once.
When Does the Racing Begin?
For most age-group Ironman athletes, certainly not during the first 10km.
Early in the marathon, you’re still managing.
Later, if you’ve paced the swim intelligently, ridden with discipline, fuelled well, and respected the opening run, you may earn the opportunity to start racing.
That’s when you can begin thinking about the athletes ahead.
That’s when maintaining your pace while others slow becomes incredibly powerful.
And if you’ve still got something left during the final kilometres?
Then use it.
There’s no prize for finishing an Ironman with a perfectly preserved energy reserve.
But there can be a very heavy price for spending that reserve at kilometre five.
Practise This in Your Brick Sessions
Race-day discipline needs to be trained.
During your longer brick sessions, don’t simply jump off the bike and see how fast you can run.
Practise the opening kilometres of your Ironman marathon.
Start controlled.
Settle into your planned intensity.
Practise your aid-station strategy.
Continue fuelling.
Pay attention to how your running changes as the session progresses.
You want to learn what sustainable feels like when you’ve already got cycling fatigue in your legs.
That experience becomes incredibly valuable on race day.
The Athletes You Pass Later Matter More
There is something psychologically powerful about running strongly late in an Ironman marathon.
Athletes who disappeared up the road during the opening kilometres begin coming back towards you.
You’re still running.
They’re slowing.
Some are walking.
You haven’t suddenly become fitter than them during the race.
You’re simply seeing the consequences of decisions made hours earlier.
That’s Ironman pacing.
Patience early gives you options later.
Final Thoughts
The first 10km of an Ironman marathon isn’t where you prove how fast you can run.
It’s where you prove how disciplined you can be.
Settle down.
Let people pass.
Keep fuelling.
Control your effort.
Don’t bank time.
And don’t panic if the pace feels almost too comfortable.
You’ve got another 32.2km to use the fitness you’ve spent months building.
Respect the first 10km.
Because if you get those kilometres right, you give yourself a much better opportunity to actually race the kilometres that matter most.
Want to Get Your Ironman Marathon Pacing Right?
You can arrive at T2 incredibly fit and still undo months of preparation with an overly aggressive opening to the marathon.
Getting your best Ironman performance means bringing your swim pacing, bike execution, fuelling, hydration, and run strategy together into one complete race plan.
If you’d like help working out how to pace your Ironman marathon—or how your run strategy should fit with everything that comes before it—I’d love to help.
Book a free, no-obligation 40-minute coaching consultation and we can talk through your training, upcoming race, pacing, fuelling, and the areas where smarter execution could make the biggest difference.
Train smart. Race strong.