Rovman Powell insists West Indies must not get too far ahead of themselves after what he saw as an "unacceptable" level of rustiness against South Africa.
The Windies won by seven wickets in Friday's T20I to take a 1-0 lead in the three-match series.
They have now won five of their last six T20Is against the Proteas, having bounced back from a three-wicket defeat at the T20 World Cup in June.
However, Powell was far from happy with what he saw, with South Africa posting a competitive 174-7 - Tristan Stubbs top-scoring with 76 and Patrick Kruger adding 44.
Powell said: "I think it's always good to go 1-0 up. We bowled well in the powerplay and though we let them off a bit, we were good with the bat.
"The guys look a bit rusty, which is unacceptable at this level.
"To be honest, a lot of talk is around the next T20 World Cup but we have to play one game at a time and see different players. We have to stay in the moment and the 2026 T20 World Cup is too far for us."
Shai Hope's 51 and Alick Athanaze's 40 got the Windies' chase off to a strong start, paving the way for Nicholas Pooran to take centre stage with an unbeaten 65, which included reeling off four straight sixes in one over.
"I just felt like Shai and Alick put South Africa under pressure in the powerplay," said Pooran, who was named Player of the Match.
"At the ten-over mark, we knew it was a better wicket and my job was simple and I just had to take on my match-ups.
"With rain around, the first ten overs were tricky when South Africa batted. Stubbs and Kruger played well, but we knew the wicket would get better."
Along with Stubbs' performance with the bat, one other bright spark for South Africa in their defeat was teenager Kwena Maphaka, who claimed his maiden international wicket.
"Maphaka has a lot of X-factor and is really young," said Proteas captain Aiden Markram. "He has hunger when you speak to him off the field and he wants to win games for South Africa."