Goals from Alfonso Pedraza and Moi Gomez handed the seventh-placed Villarreal their first LaLiga win at Camp Nou since 2008 and punctuated Barcelona's trophy-less season, finishing 13 points off the title-winning Real Madrid.
The fact Barca even finished second provided some cause for satisfaction given their start to the season, after winning only four of the opening 13 league games and sitting ninth in November, when Xavi took over from Ronald Koeman.
The 42-year-old believes, amid an expectant fan base, the time to get to work and transform the squad to his liking has officially come, now Barca have reached the end of the season.
"I keep the minutes in which people have cheered," Xavi said post-game. "It is normal, the public does not like to lose. But taking stock, we have to be satisfied. We have to be humble and see reality. Now the work of the office begins.
"We have to change things. We have to opt for titles. We have to change things. We have to improve and strengthen ourselves."
After only managing Al-Sadd for two years before taking on the coaching role at his former club, Xavi has experienced a baptism by fire upon his return to Europe, with crises gripping his boyhood club both on and off the pitch.
The Blaugrana have experienced positive and difficult moments in his first coaching role in Europe, defeating Real Madrid 4-0 at the Santiago Bernabeu but also falling meekly in the Europa League at the hands of eventual winners Eintracht Frankfurt.
On a personal level, Xavi is in a sense satisfied he has aided Barcelona in qualifying for the Champions League and salvaging their season, but is the adamant his squad must improve.
"I knew that it was coming at a complicated and difficult moment," he said. "We have improved, but not enough. We have played brilliant games, but we have to be more reliable. I am here to add value, now we have to work for next year. We have to be positive.
"We've saved a season that could have been disastrous. I'm satisfied on a personal level. We came from one of the worst moments in the club's history. A lot of things have to be changed.
"This season has gone as it has gone. The coach has changed. And now we cannot come second. We have to reinforce ourselves very well. We have to compete. We have to change many things."