Prior to City's game against Slovan Bratislava, they sat one game behind United on the leaderboard for the longest undefeated streak in the Champions League.
United had gone a staggering 25 games unbeaten from 2007 to 2009.
However, Pep Guardiola's side has now matched that tally thanks to a 4-0 thrashing of Slovan Bratislava.
Should City win their next game, United would have lost yet another record to their rivals
But, more importantly, they ensured they equalled their cross-town rivals' record.
City won't have to wait long for the opportunity to surpass United and set the bar higher as they face Czech side Sparta Praha on October 23.
Before City embarked on their remarkable unbeaten run, Ajax and Bayern Munich shared the second-longest unbeaten stretch in Champions League history with 19 games.
Ajax accomplished the feat from 1994 to 1996 while Bayern enjoyed the undefeated stretch from 2001 to 2002.
Guardiola's iconic Barcelona side of the early 2010s held the next-longest unbeaten run as they went 16 games without a loss from 2011 to 2012.
Should City go on to beat Sparta Praha and take the record for themselves, it would be yet another crushing blow for United supporters.
Since City won their first Premier League title in the 2011-12 season, they have gone on to win a staggering 18 trophies.
As for United, they have won just six.
City have also enjoyed a brighter start to this year's Premier League campaign and sit in second with 14 points.
Unfortunately for United, they lie in 13th with two wins, a draw and three defeats.