Pompey produced a performance to match the red-hot temperatures, as they secured a comfortable win at Cheltenham.
Colby Bishop was the star of the show by netting in each half, the second coming from the penalty spot after Michael Jacobs had been brought down.
The Blues played the conditions perfectly, keeping hold of the ball and using it wisely to cause their opponents plenty of problems.
Danny Cowley made a single change from the side that drew with Lincoln in the last League One outing.
It came up front, where Joe Pigott dropped to the bench to make way for Tottenham loanee Dane Scarlett.
Pompey made the more confident start in sweltering Gloucestershire, with Scarlett proving a pest in the opening stages.
Marlon Pack had a chance against his former club, but could not keep his shot down after receiving the ball from Joe Rafferty.
And Jacobs then saw his effort blocked after Connor Ogilvie’s throw had caused chaos in the Cheltenham area.
Dan Nlundulu was receiving plenty of stick from the travelling fans because of his Southampton connections.
And the forward collected the game’s first booking following a petulant booting of the ball after fouling Sean Raggett.
Then, following a needed break for drinks, Nlundulu foolishly took a swipe at Louis Thompson, but escaped any further punishment.
Bishop caught the Robins defence dithering on the half-hour mark and managed to win the visitors a corner.
And although the initial delivery from Jacobs was dealt with, the ball was soon returned to the feet of the midfielder.
His second cross from the left was nodded down by Michael Morrison for BISHOP to flick into the net.
Cheltenham improved after that setback, with Taylor Perry and Elliot Bonds both sending shots narrowly off target.
But it was the Blues who had the final chance of the half after Luke Southwood had failed to hold a cross.
That led to a scramble in the area, with the hosts throwing bodies in the path of the ball to deny both Bishop and Scarlett.
Half Time: Cheltenham 0 Pompey 1
The Blues were straight back on the attack when the action restarted and Lewis Freestone had to hook the ball behind to deny Scarlett.
Cheltenham were being put under intense pressure, with a succession of crosses – and one monster Pack throw – causing scares in their defence.
But it was some skilful play from Jacobs that led to the advantage being doubled, with the midfielder getting past Ryan Jackson in the box and drawing a crude challenge from the wing-back.
Referee Ben Toner pointed straight to the spot and BISHOP stepped up to calmly roll the ball into the bottom corner.
It might have got even better for the Blues moments later, but a 25-yard rocket from Ogilvie flew narrowly over.
Cowley introduced some fresh legs on 67 minutes, with Scarlett and Reeco Hackett making way for Pigott and Owen Dale.
And another double switch followed shortly after, as Tom Lowery and Ronan Curtis replaced Thompson and Jacobs.
There was frustration on the opposition bench and Robins boss Wade Elliott was shown a yellow card for something he said.
Pompey, meanwhile, saw out the closing stages in fairy comfortable fashion to collect a first three-point haul of the season.
Cheltenham (3-5-2): Southwood; Long (c), Taylor, Freestone; Jackson (Norton 84), Sercombe, Bonds (Adshead 68), Perry (Lloyd 78), Williams (Ferry 68); May, Nlundulu
Booked: Nlundulu, Bonds
Subs not used: MacDonald, Raglan, Brown
Pompey (4-4-2): Griffiths; Rafferty, Morrison, Raggett (c), Ogilvie; Hackett (Dale 67), Pack, Thompson (Lowery 70), Jacobs (Curtis 70); Scarlett (Pigott 67), Bishop (Mingi 88)
Goals: Bishop 30, 56 (pen)
Booked: Dale
Subs not used: Oluwayemi, Swanson
Referee: Ben Toner
Attendance: 4,649 (1,428 Pompey fans)