The Labour leader skewered the Prime Minister over the resignation of Matt Hancock in a performance that for once played to the gallery, rather than simply the argument.
There were even jokes, with Sir Keir pointedly looking at the SNP benches while repeating "the whole house" will wish the England team well on Saturday. Crisis? What crisis.
Speaking with the confidence of a man not facing a crucial week for his leadership, Sir Keir questioned why Mr Johnson had initially stood by the former health secretary only to then suggest he sacked him.
So often ready with a witty riposte, Mr Johnson could only point to the success of the vaccine taskforce – a stock answer now used to escape all criticism.
Sticking the boot in, Sir Keir embraced the nostalgia of a Tory affair scandal by saying it was evidence of there being "one rule for them and another rule for everybody else".
If the Prime Minister was already floundering, he then gave voters a headline to think of on polling day by appearing to dismiss the scandal as a “Westminster bubble” issue.
His remarks followed Sir Keir citing the case of 27-year-old Ollie Bibby, who died of leukaemia the day before the pictures of Mr Hancock were taken, with just one person at his bedside.
In response, the Prime Minster claimed “we all share the grief and the pain”, only to dismiss Sir Keir’s criticism as something only cared about the “Westminster bubble”.
Coming just one week after Mr Johnson’s “they jabber, we jab, they dither, we deliver” response to a question on low rape convictions, the Prime Minister appears to no longer be able to win the debate on puns alone.
Mr Johnson is no stranger to making offensive gaffes and it hasn’t held him back, but supporting Mr Hancock while Brits died alone is not a conventional eve of poll message.
The session was a much needed boost for Sir Keir, with the Tories quietly confident they will be able to swoop to victory in the Red Wall seat on Thursday.
On Wednesday’s the Labour leader’s spokesman confirmed Sir Keir would stay regardless of the by-election result, and having recently reshuffled his advisers, the former head of the CPS is clearly in it for the long haul.
His performance at PMQs showed promise, but Thursday will show results upon which his leadership will be judged.
The left, never knowingly not engaged in factional infighting, have been preparing to try and oust him since Sir Keir was appointed.
But to what end? Polling on Wednesday showed Yvette Cooper would be the most popular replacement, a strong MP, but one who is no friend to the left of the party.
It also showed seven in ten party members would prefer Andy Burnham as boss, which is flattering for the Manchester mayor, but also would require him to have a seat.
Ultimately the Labour leader is only going to go if there is a substantial appetite to oust him, and a realistic candidate to do so.
That isn’t the case, regardless of what happens in Batley and Spen.