#6) Nottingham Forest (42) 1977/78
On 26th November, when Nottingham Forest and West Bromwich Albion played a goalless draw, no one imagined that a year long unbeaten run had been set in motion. Forest went on to record an astonishing 42 consecutive league matches without defeat.
The side would go 26 games without losing in the 77/78 season and captured the title with 4 games to spare. They carried their form into the next season and played 16 more games without losing before succumbing to a 2-0 loss to Liverpool at the Anfield.
Off their 42 games, Forest recorded 21 wins and 21 draws. Their record would stand for 26 years before they would finally be overtaken.
#5) Barcelona (43) 2017/18
No side in the La Liga has ever gone through an entire season without losing a game. However, Barcelona came extremely close to being the first side to do so after avoiding a loss in 36 games before succumbing to a 5-4 loss to Levante in the Penultimate league match of the season.
This was their first league defeat since going down 2-0 to Malaga on April 8, 2017. They would then engineer a 43-match unbeaten run in the La Liga and eventually surpassed Real Sociedad, the previous record holders, who also ironically lost their penultimate match.
In the end though, the loss had no bearing on who would go on to win the La Liga. By the time Barcelona suffered their first loss of the season, they were already 12 points ahead of Atletico Madrid who were on second place.