Sir Keir usually runs rings around the PM, but the tables turned with the lawyer buckaroo-ed into the dock by a buoyed-up Boris.
The PM kicked off PMQs by hailing the UK’s approval of the Pfizer/BioNTech vaccine as “fantastic news”, sparking a hearty “Hear! Hear!” from his palpably fed-up backbenchers.
And while some of his Cabinet might be wheeling out the Union Jack bunting and describing the UK as “leading humanity’s charge”, the Prime Minister took a much more measured approach.
“It is by no means the end of the story, it is not the end of our national struggle against coronavirus,” the PM warned.
The party pooper even went on to tell everyone not to “get their hopes up” about the speed of the roll out.
There stands a man who has learned the hard way not to promise any more “world beating” goodies for the nation.
Re-establishing himself as the libertarian bendy banana lover we all once knew, the PM insisted the vaccine would not be mandatory because “that’s not how we do things”.
A day of vaccine victory. But not victory at all costs.
Starmer, meanwhile, was all about mature cooperation.
“Whatever our differences across this House,” he said gesturing around the chamber: “We’ve all a duty to play our part in this national effort…”
The Prime Minister asked Starmer to pay tribute to the work of his vaccine taskforce which secured the jab deal.
“Well, I pay tribute to everybody who has got us this far and we will work with all of them to get us where we need to go next,” said Sir Keir.
The Labour leader even went on to ask for a copy of the Government’s vaccine communications plan so that “we can all say the same thing in the same way to the country”.
Pffff that’s rich coming from you, thought the Prime Minister: “It’s a bit much [Sir Keir] should attack the economic consequences of the fight against coronavirus when last night neither he nor his troops could be bothered to vote for sensible balanced measures that would open up the economy and allow businesses to trade.”
Sir Keir responded with his best blow of the debate, giving the PM a death stare across the Commons: “When I abstain, I come to the House and explain.
“When the Prime Minister abstains he runs away to Afghanistan and gives the taxpayer a £20,000 bill.”
Chortle chortle. The Labour MPs liked that one. Even Boris cracked a smile.
After tackling the PM over vaccine disinformation, Sir Keir’s major gripe was over job losses and the collapse of Arcadia.
He told the Prime Minister to take it “seriously”, warning him “don't deflect” and asking him to work with Labour to develop a plan to save retail jobs.
No-one thought it possible, but Sir Keir became even more stern than usual and glared across the despatch box: “These are real people Prime Minister, with real jobs…they really need to hear from you.”
The Prime Minister knew this was his moment to unleash bombastic Boris.
At rapid fire speed, he replied: “We're of course supporting every job we possibly can, as well as supporting every life and livelihood with a £200 billion programme.”
Swivelling to look at the Speaker, the Prime Minister bellowed: “I’d take him more seriously, frankly, if he actually could be bothered to vote for a moderate programme to keep the virus down and open up the economy.
"When it came to protecting the people of this country from coronavirus at this critical moment – he told his troops to abstain.
“Captain Hindsight is rising rapidly up the ranks and has become General Indecision!"
Oh, how the Tories did guffaw!
Bojo showed he’d definitely got his mojo back, adding: “That’s what’s happening I’m afraid to [Sir Keir]. He dithers, we get on with the job.”
Guffaw! Guffaw! Guffaw!
As the Prime Minister’s head ballooned to Violet Beauregarde proportions, the Tory MP for Wakefield got to his feet to praise his “mighty majority” and “bold vision”.
Imran Ahmad Khan went on to beg the PM to make his constituency the home of his new infrastructure bank and to “restore my city’s glory”.
One charming interlude came from Plaid Cymru MP Liz Saville Roberts who popped up on the Chamber’s screens to say: “This really is a ray of light in dark times,” before bemoaning the “rail betrayal” of Wales.
Now, that’s more like it!