Ronald Koeman believes Alan Pardew has turned Crystal Palace into a much tougher side than the one Southampton so easily overcame a month ago.
Saints' 3-1 triumph at Selhurst Park on Boxing Day proved the catalyst for change in south London.
Neil Warnock was promptly sacked by the struggling Eagles, who head into Saturday's FA Cup fourth-round tie at St Mary's riding the crest of a wave.
The appointment of Pardew has brought with it an impressive change in fortunes at Palace, with their former player overseeing three successive wins in all competitions.
"They have a spirit in the team, the confidence and they have had a great start (under Pardew)," Koeman said of Palace. "The first win [against Dover] was normally an easy FA Cup round for them, but the first victory in the Premier League against Tottenham Hotspur gave everybody confidence.
"At the moment they are more difficult to beat than over Christmas on Boxing Day.
"They have new players and a new manager and that always means some changes in tactics or organisation in the team and I think the manager is more happy than he was before, and that's important."
Palace sit 13th in the standings ahead of Pardew's trip to the club he led to the Johnstone's Paint Trophy in 2010.
Jose Fonte started that 4-1 defeat of Carlisle and will captain Saints this weekend as they continue their campaign to reach Wembley for the first time since then.
"I am lucky," Koeman said. "I don't have a lot of numbers of players to think about to make changes. The players who wasn't available in the last week are still not available for this weekend.
"That means we have 17 or 18 players and of that 17 or 18 players we have already five or six Under-21 players. There is no time and no reason to think about making changes and we will put out the strongest team we can."
Toby Alderweireld, Victor Wanyama and Morgan Schneiderlin are among those unavailable, joining long-term absentees Sam Gallagher and Jay Rodriguez in the treatment room.
International commitments mean Sadio Mane, Emmanuel Mayuka and Maya Yoshida further reduce numbers, but Saints do have the momentum of a eight-match unbeaten run on their side and a sell-out St Mary's crowd.
"We had some days off this week, we didn't play during the week," Koeman said. "The players are back in a good freshness and in a mental way I think the players are very strong because we are winning. We had a great week last week with very good results in difficult games and we like to go on."
Southampton's impressive performances, coupled with the imminent return of key players, mean Koeman is unlikely to dip into the transfer market before the window closes.
The Dutchman has already brought in compatriot Eljero Elia on loan from Werder Bremen, but does not expect to add anyone else.
"That was a little bit the question in this period," Koeman added. "We know that we have a little risk at the moment. If something happened now, then it will be difficult, but normally in two or three weeks we have everybody back and then we don't need somebody.
"I don't like to bring in a player for two games, then we have still more under-21 players. I don't like to talk to a player coming in and say, 'OK, now at the moment we have some problems -- I am happy to bring you in, but in three weeks we will have everybody available.'
"Then that player is not one of the squad that you need or it's a player with a future in the club and that's different, but now at the moment we don't have any update about that."