Alexandre Lacazette rode to Arsenal's rescue with the winner from the bench at Brighton and Hove Albion as a 1-0 success made it back-to-back Premier League victories since Christmas.
A seven-game winless run in the league was ended on Boxing Day as the Gunners beat Chelsea, although Mikel Arteta's men remained in 15th place after a dismal start to the season.
Rather than build on that triumph, a further setback appeared likely for a time at the Amex Stadium on Tuesday against Brighton, whose only prior home league win in 2020 had come on Arsenal's previous visit back in June.
But Lacazette, who lost his place in the XI to fit-again captain Pierre-Emerick Aubameyang, scored 21 seconds after his introduction as a substitute to settle a key clash in the bottom half in Arsenal's favour.
There was little in the first half to suggest Arsenal had brought forward any momentum from the Chelsea game, with Brighton well on top but themselves missing a cutting edge.
Bernd Leno watched Alireza Jahanbakhsh lash the best early chance over with the outside of his right boot, before the goalkeeper was belatedly called into action by the same man with the first shot on target eight minutes before the break.
Arsenal survived a goalmouth scramble within a minute of the restart, but they finally provided a threat on the counter soon after and Robert Sanchez blocked from Aubameyang at point-blank range.
An improved spell saw Gabriel Martinelli drive just over and the arrival of Lacazette on 66 minutes prompted the breakthrough.
A storming run down the right from Bukayo Saka created space for Lacazette, who was able to control in the centre with his first touch and fire decisively beyond Sanchez.
Only an apparent injury to Saka in the closing stages could put a dampener on a much better Arsenal second half.
What does it mean? Rollercoaster 2020 ends on a high
Arsenal have had quite the ride in the past 12 months. They were similarly struggling in the Premier League a year ago but recovered to achieve a respectable eighth-place finish while crucially winning the FA Cup.
The 2020-21 campaign has been more testing still for Arteta, yet their first league win against Brighton since 1981 took the Gunners up to 13th, now nine points clear of danger.
Brighton remain very much in peril, meanwhile, having become the first team ever to complete a calendar year in the Premier League while winning just once at home.
Lacazette looks the part
It figured that Arsenal should only find the net after calling for Lacazette. No player in the Premier League has scored the opening goal in a game as often as the Gunners striker this season (five times).
His swift strike was also the fastest league goal by an Arsenal substitute since Opta records began in 2006-07.
Aubameyang problems persist
Skipper Aubameyang had missed the biggest chance of the match prior to Lacazette's appearance, but an anonymous first half was more concerning as he failed to justify his selection.
The Gabon forward had just 12 touches before the interval, of which as many were in Arsenal's box as Brighton's (one apiece), as the visitors failed to register a first-half shot on target for the fourth time this season.
Arsenal are on the road against a side below them in the table again on Saturday as they visit West Brom. Brighton host Wolves earlier the same day.