Augustus Kargbo floats the ball into the middle, Yuki Ohashi meets it with a perfect downward header but Walker somehow contorts in the air, changing direction and getting down to his right to palm the ball up and onto the face of the crossbar when it seemed the ball was almost beyond him.
Heading to penalties...published at 21:36 British Summer Time
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As it stands, Gillingham v AFC Wimbledon, Leyton Orient v Wycombe, Salford v Rotherham and Stoke v Walsall are the four 19:45 BST kick-offs heading straight to penalties.
Ipswich are huffing and puffing in the later kick-off - George Hirst is off the bench to have a sight of goal but can't get his shot on target after a heavy first touch.
It's the visitors who are finishing the stronger at Ewood Park, but a deep free-kick to the back post is nodded too close to Rovers keeper Nick Michalski.
Blackburn have huffed and puffed but haven't opened up the visitors in the second half... yet.
Elsewhere in the EFL Cuppublished at 21:28 British Summer Time
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#bbcfootball
Ryan Loft has made it 2-0 to Cambridge at Bristol Rovers, Gillingham have levelled against AFC Wimbledon to make it 1-1andCharlton are still leading Stevenage 2-0 as are Reading at Portsmouth.
Port Vale lead Blackpool 1-0 thanks to Mo Faal's goal.
We're still waiting for goals in the games between Stoke and Walsall, Salford v Rotherham and Leyton Orient v Wycombe.
Middlesbrough fans are making their feelings very clear. This was not good enough.
Doncaster, newly promoted from League Two, made 11 changes and looked significantly better than Boro in the early stages, with deflected strikes from Ben Close and Damola Ajayi giving them a deserved 2-0 lead.
Rob Edwards' men did work keeper Ian Lawlor several times and Delano Burgzorg thumpted the post, but Robbie Gotts cracked a late third and Thomas Nixon stroked the fourth.
The visitors really might have had more before the final whistle was greeted with a chorus of boos from the fans who had only remained in order to do so.
'Massive confidence boost'published at 21:26 British Summer Time
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Plymouth 3-2 QPR
Brent Pilnick BBC Sport at Home Park
The comeback is indeed complete - and Argyle are fully worth their lead.
Young striker Owen Oseni has been in the right place at the right time to get a double on his debut for Argyle.
Having lost their first two League One games of the season this is a massive confidence boost for the hosts - albeit against a very under-strength QPR side.
GOAL: Plymouth 3-2 QPRpublished at 21:25 British Summer Time
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Owen Oseni (78 mins)
Comeback complete...
Caleb Watts' ball into the middle is turned in from close range by Owen Oseni for his second for the club on his full debut on a memorable cup night at Home Park.
It's Oseni's last involvement before being replaced by Bim Pepple.
GOAL - Wrexham 1-3 Hullpublished at 21:25 British Summer Time
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Matt Crooks (81 mins)
Game over surely! Matt Crooks is off the bench to get Hull's third, stabbing in from close range after Kasey Palmer worked the ball across from the left.
GOAL: Middlesbrough 0-4 Doncasterpublished at 21:25 British Summer Time
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Thomas Nixon (90 + 6 mins)
An absolute rout.
Thomas Nixon latches onto a loose ball in the Boro box, drops a shoulder, and strokes a lovely low finish with his left foot, to Tom Glover's right and inside the far post.
Into the last 15 minutes at The Hawthorns and Derby are starting to threaten for the first time all night. No real clear chances yet but the pendulum is swinging their way a bit.