Rantala scored her third of the season, but two goals from Lauren James, as well as strikes from Sam Kerr, Aggie Beever-Jones and an unfortunate own goal from Courtney Nevin led to defeat for the travelling Foxes, who remain seventh in the standings with eight points.
Willie Kirk made three changes from his last WSL side, that drew 1-1 with Tottenham Hotspur, with Aimee Palmer, Julie Thibaud and Aileen Whelan all coming into the starting XI, while Josie Green, Missy Goodwin and Hannah Cain all dropped to the bench.
Things got off to a poor start for the Foxes, who found themselves 2-0 down after a matter of minutes, both times through defensive errors. James opened the scoring when she latched onto a costly backpass from midfield before forcing a second when Nevin turned the ball into her own net after Janina Leitzig saved the initial shot, but caused the ball to deflect off of her Australian team-mate.
After a difficult opening period, City looked to steady the ship, and despite Chelsea still posing a threat on the break, were starting to look more comfortable, and scored their first ever WSL goal against the current champions after 26 minutes.
Controlling and turning brilliantly, Lena Petermann ran at the hosts' defence and pick out Rantala on her left, who fired an effort past Ann-Katrin Berger to score her third goal of the 2023/24 campaign.
Sadly, the home side restored their two-goal advantage 15 minutes later through Australia international Kerr, but once again, the Foxes responded well and halved the deficit just before the interval when an Aimee Palmer free-kick was bundled home by Tierney.
Just before the hour mark, the Blues scored again, and it was another City mistake at the back that allowed them to take advantage, when a pass back from Rantala was mis-controlled by Sophie Howard, giving James the chance to break through and add a fourth; a second for herself.
Kirk replaced tired legs and introduced the likes of Goodwin and Remy Siemsen to try and keep pushing Chelsea until the end, and the away side almost scored a third goal themselves when Nevin linked up with Janice Cayman to have a strike at goal, but the curling left-footed effort was claimed by Berger.
Two minutes from the final whistle, the hosts scored a final goal when a ball over the top was headed by Beever-Jones, past Leitzig, to round off the scoreline in London. Despite the loss, there were positives to take for City, who scored twice as Kingsmeadow, but the Manager will be wanting to improve on their defensive side of the game after the international break.
With a week off now, Leicester are next in action when they take on Brighton & Hove Albion at Broadfield Stadium in the WSL on Sunday 10 December (2pm GMT kick-off).