After two consecutive draws, Blackstenius' dramatic match-winner kept the pressure on in the Women's Super League, helping Arsenal climb to third and reduce the gap at the top to five points — although the rest of the division play tomorrow.
Arsenal started the better side at the Emirates, with Olivia Smith lively down the left. Lotte Wubben-Moy greeted Mariona Caldentey's cross in the 15th minute, but was denied by the crossbar.
Building on their early momentum, it was not long until the Gunners made Liverpool pay. Smith drove inside, beating three Liverpool players before nestling a deadly strike from 20 yards into the bottom corner.
Inadvertently, Alessia Russo nearly doubled the home side's lead in the 26th minute. Her cross from the right almost dipped underneath the crossbar.
Liverpool had been passengers for the first half an hour but managed to draw level against the run of play when Mia Enderby won the second ball from Anneke Borbe’s goal kick and found Beata Olsson, who slotted away neatly.
The leveller gave Liverpool a burst of life in the 15 minutes before the break. However, Arsenal heeded the warning and created chance after chance in a one-sided second half.
Two big opportunities fell for Russo in as many minutes, as she used her agility to wiggle through on goal and force a great save from the Liverpool goalkeeper, before putting the other wide of the target.
Arsenal boss Renee Slegers made three alterations after an hour, with Caitlin Foord, Stina Blackstenius and Katie McCabe entering the fray as they sought the winner.
Blackstenius almost made the impact when she got on the end of a poor backpass to beat Kirby, but Gemma Evans recovered with a brilliant piece of defending.
Blackstenius refused to let another opportunity slip away. She latched onto Emily Fox’s incisive ball over the top and wrapped her left foot around it from outside the box, firing into the top corner for her fifth WSL goal of the season.
Arsenal were rewarded for their zeal as they leapfrogged Manchester United with three points. Next-up for the Gunners is Dutch side Twente in the Champions League on Tuesday.