The result left Barca four points clear at the top of the Primera Liga with one match to go before the halfway mark in the season. Arch-rivals Real Madrid are 13 points adrift of the leaders back in sixth place after a 0-0 draw at Villarreal.
Osasuna took the lead when French midfielder Ludovic Delporte scored with a marvellous curling free kick on the half hour but Santander striker Antonito poached an equaliser on the stroke of halftime to end the Navarrans' perfect home record.
"There is nothing to worry about," said Osasuna coach Javier Aguirre. "We played well, but just lacked the scoring touch up front."
Champions Barcelona had continued their imperious progress with a 2-1 victory over city rivals Espanyol on Saturday to chalk up their 15th straight win in all competitions.
Frank Rijkaard's side have 43 points from 18 games, while Osasuna follow on 39, six ahead of Valencia who were held to a 0-0 draw at Atletico Madrid in Sunday's late match.
Deportivo Coruna are in fourth a further point behind following their 2-1 win at Athletic Bilbao on Saturday, one clear of Villarreal and two ahead of Real Madrid.
Real, missing the suspended David Beckham but with Jonathan Woodgate back from injury for his first start in two months, enjoyed the better of the opening exchanges at El Madrigal.
FLUENT FOOTBALL
Villarreal soon got into their stride and played the more fluent football with Juan Roman Riquelme leading the way.
The Argentine international almost put his side ahead when he shaved the post with a curling shot after a marvellous piece of interplay with fellow countryman Juan Pablo Sorin and striker Diego Forlan went close with a well struck volley soon after.
Zinedine Zidane replied for Real with a rasping drive, but Villarreal keeper Sebastian Viera made a superb fingertip save to turn the Frenchman's shot around the post.
Real suffered a major blow when leading striker Ronaldo went off injured with what looked to be a recurrence of a recent calf strain 12 minutes before halftime.
With Italian striker Antonio Cassano remaining in Madrid to regain his fitness after signing from AS Roma, coach Ramon Lopez Caro decided to give his other new signing Cicinho his debut.
Villarreal continued to hold the upper hand in the second half and Forlan spurned a great chance to give them the lead when he scooped the ball over the bar after Jose Mari had threaded a neat pass through Woodgate's legs.
Woodgate, who had showed occasional glimpses of the form that caused Real to sign him at the start of last season, was fortunate to stay on the pitch when he brought down Jose Mari as the striker raced clear in the 73rd minute but he escaped with a booking.
Both defences remained firm for the remainder of the game and the two sides had to settle for a draw.
At the other end of the table, basement side Alaves were left three points adrift of fellow strugglers Bilbao after losing 2-0 at home to Real Zaragoza, the goals coming courtesy of in-form strike partners Diego Milito and Ewerthon.
