World number seven Berdych claimed he had delivered his worst performance of the year in going down 6-1 6-1 to Stanislas Wawrinka in the opening Group A match at London’s O2 Arena on Monday.
The Czech failed to find any rhythm and won just five points on his opponent's serve in a one-sided encounter that lasted less than an hour.
While Berdych, who has now started the season-ending event with a defeat on five successive occasions, could yet qualify for the semi-finals, he is aware the odds are against him with contests against world number one Novak Djokovic and US Open winner Marin Cilic to come.
Speaking in a post-match news conference, Berdych said: "Unfortunately it was my worst match of the whole season, and I kept it for the start here in the World Tour Finals.
"My game is about hitting the ball nice, clean – then you can create something. But that's what I didn't have today at all. I hit so many frames.
"I'm in the worst possible situation that I can ever be. I'm going to face Marin or Novak first, in the end playing both of them, and the only chance to qualify is to beat them.
"It's almost a mission impossible. But I don't know – let's try. I just need to be ready for it, need to be prepared, try to play better."
Berdych had recently expressed a desire to strike up a partnership with fellow Czech Ivan Lendl, who helped Andy Murray win two grand slam titles and an Olympic gold medal.
However, Lendl rejected the chance to move back into coaching and Berdych said: "I think working with him, that's over for now definitely.
"I don't know what has to be the change to change his mind, but it's how it is.
"I just respect his decisions. There is no reason to still be looking back. You always have to look forward and keep moving."
Australian Open champion Wawrinka, meanwhile, was able to reflect on a welcome return to form, after arriving in London having won just one match in his previous four tournaments.
"I didn't expect to win that easy in the score, for sure. But I was ready to play well," said the Swiss.
"I did a great week of preparation. The start of the match was really important. That changed the match completely.
"When I feel good on the court, I'm ready to beat everybody."