A first-half strike from John Guidetti put Barca's record in jeopardy at the Camp Nou on Sunday, but Luis Suarez pulled his side level in the 72nd minute before a Lionel Messi free-kick gave the Catalans a 2-1 victory.
Barca now have 18 wins and three draws in La Liga, while they managed 17 victories and four draws to open the 2009-10 campaign.
21 - Barcelona have equaled their longest unbeaten start to a league campaign in their history (W18 D3); under Pep Guardiola in 2009/10 (W17 D4 L0). Unstoppable. pic.twitter.com/jrCVXGXuWD— OptaJose (@OptaJose) January 28, 2018
The comeback also gave Barca 12 points gained from losing positions this season — more than any other club in La Liga.
The Catalans will then look to break their club record against Espanyol next Sunday by stretching their unbeaten run in the league to start this season to 22 matches.