Paul Cook’s departure just 25 days after steering Pompey to League Two glory came as a shock, with a new manager having to be identified.
It was Jackett who was elected to be the successor as the Blues prepared for life back in the third tier ahead of 2017-18.
After the regulatory meeting with the press, it was time to get down to business and draw up a list of targets.
Pompey were already behind their rivals in the window, forced to play catch up.
Cook’s parting gift, of course, was to have Nathan Thompson all but signed on the dotted line, with Jackett giving his seal approval.
But then it was up to the new manager to get his own players through the door.
Tareiq Holmes-Dennis was the next arrival from Huddersfield on loan and then Luke McGee for an undisclosed fee from Tottenham.
But it was 48 hours later when the marquee signing of the summer arrived.
Brett Pitman was cajoled to drop from Championship Ipswich to Fratton Park for an undisclosed fee.
At the time, it was regarded as a real coup. Pitman had a reputation as one of the deadliest marksmen outside the top flight, having scored 100 times for Bournemouth – 14 of which when they were promoted to the Premier League in 2014-2015.
While he may not have been as prolific at Portman Road over two seasons and was approaching 30, the feeling was moving down a tier would help him rediscover his touch.
And as Pitman prepares to take on the Tractor Boys for the first time since departing when they visit PO4 on Saturday, the Blues are still getting their worth out of him.
In his maiden campaign, he proved as rampant as many predicted. From an opening-day double in a 2-0 win over Rochdale, Pitman went on to plunder 25 goals and finish second in the League One goalscoring charts behind Peterborough's Jack Marriott.
The Jersey-born forward had to settle for a bit-part role for large chunks last term.
He lost his berth leading the line to Oli Hawkins, but a revival in the number-10 role towards the end of the campaign helped the Blues to Checkatrade Trophy glory and finish fourth in the table. Impressively, he was still the club’s joint-second top scorer with 13.
This campaign, summer signings Ellis Harrison and John Marquis have been Jackett’s favoured pairing in the central attacking positions.
Now Pitman might not be the indispensable player he once was, but he’s still got a part to play in the promotion push. From 15 games, he’s scored four goals – all of which have been crucial.
He’s accrued the Blues four league points to date. A last-gasp penalty earned a 2-2 draw against Burton, while a superb header clinched a 1-0 success over Bolton.
And in cup competitions, he bagged the only goal against Crawley in the EFL Trophy and another effort in the dying embers to deliver a 2-1 FA Cup second-round success over Altrincham.
Out of contract this summer, it could well be Pitman's final season at PO4. Nevertheless, the master stroke which was raved about at the time is still having its rewards.