Pardew, who was returning to the club where he was sacked as manager in August 2010 when the Saints were still in League One, believed that the home side were fully worthy of their 2-0 victory courtesy of goals from Adam Lallana and Gaston Ramirez.
"We're worried, of course we're worried, because we are Newcastle United and we've really got that dressing room to take into Wednesday night," Pardew told reporters as the Magpies slipped to 14th place in the table, just four points above the relegation zone.
"It's not like we can add four or five players from the squad into that group. That is our group and they have been soundly beaten today and are going to another tough place [on Wednesday against Stoke].
"We have three days to try and lift the team to try and get ready for another tough game."Meanwhile, his counterpart at Southampton Nigel Adkins was hugely pleased his players' performances, which saw them pick up only their third league victory of the season and climb out of the relegation zone in the process.
"We scored two, but could have scored some more," said Adkins, who had come under pressure for his job before last week's 3-1 victory at QPR.
"The crowd were great, the players were great and we got a clean sheet. We've been progressing all the way through.
"Last week I spoke about a growing maturity about the group of players and I think we're progressing well. Our confidence has been good since the start of pre-season.
"But you've got to get yourself ready as quickly as possible to reach the level the Premier League is at. The players are doing that and doing that very well at this moment in time. We know we're in the hardest, toughest and most desirable league to be in.
"We worked very hard to get here and we'll continue to keep working hard. We have a forward momentum about ourselves."
At the hear of the Saints' victory was club record signing Ramirez, who was making only his third appearance since his comeback from a leg injury.
"Gaston missed the start of the season as it was before he signed and then he got injured," Adkins reflected.
"Obviously you've got to get used to it all. He hasn't lasted the full game today but when he was on the field of play he was exhilarating."