Tonda Eckert made three changes to the team that started on Wednesday in the home win against Sheffield United. Southampton hadn't won at Fratton Park in the league since 1976 before today's match.
Sticking with a 4-2-3-1 formation, the Saints looked more balanced from front to back. James Bree started the match at right back, with Matsuki a surprising starter ahead of Tom Fellows.
Jack Stephens kept his place at centre-back alongside Taylor Harwood-Bellis, displacing both Nathan Wood and Joshua Quarshie.
Wantaway striker, Adam Armstrong, returned at the expense of Ross Stewart, who played sixty minutes on Wednesday night.
Southampton were unlucky not to be ahead in the eleventh minute when Finn Azaz slid Adam Armstrong in. Armstrong kept his shot down from 12 yards out but was unable to steer the ball wide of the keeper, who saved well with his feet.
Only a great save by Nicolas Schmid in the nineteenth minute denied Armstrong again. The Saints striker struck his volley well from close range, but the Pompey keeper did well to make a reaction save.
Millenic Alli shot tamely wide for Portsmouth in the 22nd minute when he should really have hit the target. The ball fell to him after the Saints failed to clear the ball fully from a corner.
Welington was in the wars in the first half; a nosebleed forced him off for a few minutes. He made an excellent block on a Chaplin volley midway through the first period, deflecting the ball over the bar for a corner.
Half-Time: Portsmouth 0-0 Southampton
Léo Scienza put Saints ahead in the 57th minute, finishing coolly after being put through by Finn Azaz. After running the full-length of the pitch, Scienza danced in front of the joyous Southampton fans in the away end.
Portsmouth drew level in the 76th minute as Southampton conceded from another set piece when Ebou Adams bundled in from under the bar. The ball looked to have come off Adam's hand, but the Saints will be disappointed that the corner wasn't dealt with in the first place.
Full-Time: Portsmouth 1-1 Southampton
Goalkeeper and Defenders
Daniel Peretz (GK) - 6/10 - Did not cover himself in glory on the Portsmouth equaliser. He should have been much stronger under his own crossbar.
James Bree (RB) - 7/10 - Started strongly in both defensive and attacking transitions. Looked composed despite coming straight into the team after his loan spell at Charlton Athletic. An excellent performance on his return from Charlton.
Taylor Harwood-Bellis (CB) - 7/10 - As solid as ever in the heart of Southampton's defence. Unlucky to see the ball bounce off his knee directly into Adam's path for the Portsmouth equaliser.
Jack Stephens (CB) - 7/10 - Made a fantastic tackle to deny Colby Bishop a clear shot on goal on the quarter-hour mark. Showed determination and commitment as expected.
Welington (LB) - 6/10 - In the wars in the first half, a nosebleed forced him off for a few minutes. Made an excellent block on a Chaplin volley midway through the first half. A couple of wayward passes late on got Saints fans' hearts pounding - not in a good way.
Midfielders
Flynn Downes (CM) - 8/10 - Played deep at the base of a midfield diamond and was often isolated and exposed there. Downes epitomised the determination that eventually earned Southampton the point, and his challenge with Ogilvie was worth an extra point in itself.
Caspar Jander (CM) - 7/10 - Busy but unable to get on the ball often enough to contribute in attacking transitions.
Attackers
Léo Scienza (AML) - 6/10 - Hardly involved until he scored. Not a classic Scienza performance, but Portsmouth doubled up on him for most of the match.
Finn Azaz (AMC) - 7/10 - Played centrally behind Armstrong and was influential in the early stages. Put Armstrong clean through on goal in the eleventh minute. Plucked the ball out of the sky with a sublime touch before putting Scienza through for the goal. Brilliant and frustrating in equal measure.
Kuryu Matsuki (AMR) - 7/10 - Energetic start, but a little too enthusiastic in the challenge early on, giving consecutive fouls away. An unbelievable backheel to Finn Azaz started a great move, which ended in Armstrong having a golden chance to put the Saints ahead. Justified inclusion in the starting eleven.
Adam Armstrong (CF) - 6/10 - Almost put Southampton ahead twice within the first twenty minutes. Only two good saves by Nicolas Schmid denied him. Worked very hard along the front line. Paid to score goals.
Substitutes:
Ross Stewart - 6/10
Shea Charles - 8/10
Tom Fellows - 6/10
Jay Robinson - 5/10