Saints beat the transfer deadline by a whisker last night to complete a major double swoop, signing defender Toby Alderweireld and winger Sadio Mane.
The club finalised both deals right at the very last moment, taking their spending for the summer close to £60m and giving their squad a significant boost going into the rest of the season.
Saints also kept hold of Morgan Schneiderlin and Jay Rodriguez, despite interest from Tottenham in both players, making it a fine deadline day for them.
Belgium international Alderweireld, who can play at right-back or centre-half, joined on a season-long loan from Atletico Madrid, with an option to buy next summer for a fee believed to be €8m (£6.3m).
Senegalese star Mane signed a four-year contract, after Saints paid £10m to Red Bull Salzburg for the winger’s services.
Alderweireld revealed it was Saints boss Ronald Koeman who had persuaded him to move to the club.
“I had a good talk with the coach,” he told the club's website. “First of all, it was very important for me to play this season and the coach gave me a good solution for that.
“The trainer likes how I play and really wanted me to come here, which is what convinced me to come. I really wanted a trainer that believes in me, because that’s important.”
Koeman added: “He is a strong defender, and is also very good at building up the play when we play out from the back.
“He played in the top league in Spain and against top teams in Europe, so he has a lot of confidence and experience, and he has a big future because he is still young.”
On Mane, Koeman said: “Right from the first meeting I had with Les Reed, when it was clear that we would have to change a lot, Sadio was on our list of potential players.
“I know the player because last season Ajax Amsterdam played against Red Bull Salzburg in Europe, and I saw him playing and I was impressed with his qualities and with the physicality that he showed.
“He can play in different positions in the attack – he can play on the left or right side and also as a number nine. It is incredible how many goals he has scored from his position, and I hope that he will do the same for us.
“With the way that we play and the fact that I know him very well, this is a good step forward for him.”
The arrivals represent a coup for the club, who had identified them as their top two targets heading into the final stages of the window, and they are believed to have beaten stiff competition from elsewhere to sign them.
Saints have now added eight players to their first-team squad in the transfer market this summer, at a combined cost of nearly £60m.
Alderweireld and Mane join Fraser Forster, Florin Gardos, Ryan Bertrand, Dusan Tadic, Shane Long and Graziano Pelle at the club.
The board are confident that those captures, combined with what they already had in place, will fill the void left by the departures of Rickie Lambert, Luke Shaw, Adam Lallana, Dejan Lovren and Calum Chambers.
As well as seeing two new arrivals, Saints fans could also celebrate the news that another duo, Schneiderlin and Rodriguez, stayed put.
Tottenham had been interested in both players and, although they had effectively given up hope of signing Schneiderlin, they did make a big push yesterday for Rodriguez.
Spurs are understood to have made multiple attempts at striking a deal, including a cash-plus-Andros Townsend package, but were consistently rebuffed by the Saints board.
Saints also kept hold of midfielder Jack Cork, despite interest from a number of clubs, such as Crystal Palace and Swansea.
Cork is entering the final year of his contract, and no new deal is in the pipeline, but Koeman sees him as a valuable squad player for the season ahead.
Artur Boruc also remained at the club, despite Saints having been willing to part ways with him, after Forster came in as the new number one.
Boruc has not been involved in any of the matchday squads this season, but Koeman said his situation would be reassessed if he remained at St Mary’s after the deadline.
There were some outgoings, though, with Gaston Ramirez joining Hull and Jos Hooiveld moving to Norwich, both on season-long loans, while Jack Stephens moved to Swindon until the end of January and Saphir Taider's loan spell was, as expected, terminated early.
Alderweireld began his professional career at Ajax, making 185 appearances for the Dutch giants and winning three successive Eredevisie titles, from 2011 to 2013.
Atletico Madrid signed him last summer for a fee of about £6m, with the defender agreeing a four-year deal at the Spanish side.
He was part of the team that won the La Liga title last season, but made just 12 appearances in the competition, and 22 in total.
Alderweireld has been capped nearly 40 times for Belgium, and made four appearances in this summer’s World Cup, helping his country reach the quarter-finals.
Mane began his career with French side Metz, coming through the academy system.
He made his first-team debut in the 2011/12 season and, after two impressive campaigns, he was signed by Austrian club Red Bull Salzburg.
Mane has made 88 appearances for the team, with an outstanding return of 46 goals.
He has been capped 15 times for the Senegal national side, while he also represented his country at the 2012 Olympic Games.