Salah tucked away his league-leading 24th goal of the campaign to put Liverpool ahead at Villa Park in the 29th minute on Wednesday night, only for the leaders to fall behind by halftime following a Youri Tielemans volley and an Ollie Watkins header.
Alexander-Arnold ran onto an inside pass from Salah and drove in a shot that deflected past Villa's Argentine goalkeeper Emi Martinez in the 61st minute as Liverpool salvaged a point, avoiding what would have been just a second league defeat of the season.
It remains to be seen whether this was a good point for Liverpool in one of the toughest away fixtures in the league or two more dropped points, a week after a 2-2 draw at local rivals Everton.
"We desired more," Liverpool manager Arne Slot said, "and that is the only thing we can blame ourselves for a few times now — we did not get what we deserved. We must not make a habit of that."
Slot's side have now played a game more than second-placed Arsenal, who appear to be the only other realistic challenger for the title.
The Gunners play first out of the top two at the weekend — at home to West Ham United on Saturday — and have the chance to trim the lead to five points before Liverpool meet Manchester City.
Liverpool are seeking a 20th top-flight championship to tie the record of Manchester United.
Salah is spearheading Liverpool's title charge. Not only is the Egypt forward the league's top scorer, with five more than nearest challenger Erling Haaland of Manchester City, he has more assists than anyone else with 15.
Should Arsenal wind up reeling in Liverpool, the Reds may regret a big miss from Darwin Nunez after the Uruguay striker came on as a substitute. Szoboszlai ran through a squared the ball to Nunez, who had an open goal at which to aim with a left-footed shot, but he blazed high and wide.
"Darwin ... it was not his best leg, he's right footed, of course, but it was still a big chance," Slot said.
"I was hoping that he could have got another one, because a player like him probably wouldn't miss two chances in a row.
"It was a great game but I am not happy with the result."
Villa then had chances to win it, with Morgan Rogers shooting over and substitute Donyell Malen driving just wide with one of the last kicks of the game.
"Liverpool is the best team in the Premier League and Champions League but we competed," Villa boss Unai Emery said.
"... I think the result was fair for both teams because they had chances, and we had chances at the end of the match."
Villa, who had lost just once at home all season in the league, stayed ninth and four points off fifth - enough to qualify for next season's Champions League.
With PA.
