The Navarrans are unbeaten, taking seven points and conceding just one goal, since the turn of the year, which has lifted them to the relatively comfortable position of 13th in the Primera Division - six points clear of the relegation zone.
"The fact we have been able to turn the situation around by working hard has given us confidence," Andres told a press conference.
"We have reached a point where whoever ends up playing does a good job and the effect that has had on the team is easy to see."
Andres felt things were looking bright for his side again after a poor start to the campaign, but vowed the players would continue to work hard.
"We are now starting to pick up the points we need to stay up, and we've got over the 20-point hurdle," he said.
"But we cannot afford to relax. We need to keep reminding ourselves that if we don't keep playing well, we will have a torrid time."
Athletic lost their opening game of 2014, at Real Sociedad in the Basque derby, but have scored 10 goals in their last two league games, recording 6-1 and 4-2 wins over Almeria and Valladolid respectively.
Against Osasuna they will be looking to maintain their grip on fourth place by returning to winning ways after Thursday night's frustrating 1-0 defeat at Atletico Madrid in the first leg of their Copa del Rey quarter-final tie.
Ernesto Valverde's side were particularly annoyed that Diego Costa was allowed to stay on the pitch during the game, despite a number of infringements after picking up a yellow card.
"He (Costa) did enough to get sent off. He did everything he was allowed to get away with," defender Andoni Iraola said to reporters.
Iraola added that his side also "need to focus on playing better" in the second leg at San Mames.
The Basques will welcome back Iker Muniain to the side on Sunday now that the midfielder, who grew up in Pamplona although never played for Osasuna, has recovered from a hamstring injury which kept him out of the last two games.
Mikel Rico and Mikel San Jose also return from suspension, while the hosts are able to recall Andres to the squad after he missed the 0-0 draw at Granada last weekend through suspension, with stand-in goalkeeper Asier Riesgo impressing in his absence.