Petermann opened the scoring just before the break with a left-footed effort from range, before Rantala doubled Leicester's advantage immediately after the restart, but the late show came from Brighton, as Terland netted her sixth and seventh goals of the season to level the Barclays Women's Super League encounter.
Willie Kirk made just one change to the side that were beaten 5-2 by Chelsea before the recent international break, with Josie Green coming in for Courtney Nevin, but it only took 12 minutes for the Australian full-back to be introduced after CJ Bott was withdrawn through injury.
Both teams found it tough to adjust to the adverse weather conditions in the early stages but it was City who fashioned the first real chance of the game when Janice Cayman crossed the ball into the path of Petermann but her directed header flashed just wide of the near post.
Brighton soon found themselves in the ascendency but Janina Leitzig was able to get behind anything they hit towards goal, and the next opening was from the Foxes. Winning the ball high up the pitch, Leicester dedicated numbers forward allowing Rantala the chance to pick out Nevin - the defender's effort deflected behind for a corner which came to little.
Just before half-time, the deadlock was broken by German forward Petermann, who managed to hit a sweet left-footed strike past Sophie Baggaley and into the top corner to score her third of the campaign.
After the interval, it only took the Foxes 20 seconds to double their lead; Rantala finding the target. Good build-up play between Petermann and Nevin led to the ball finding Sam Tierney, who did well to pick out the Finnish international inside the box, curling an effort onto the postage stamp.
The next half-an-hour saw Leicester steady the ship. Brighton, being two goals down, tried to push their way back into the game, but physical challenges and clever fouls allowed the visiting side to calm the game down and remain in control initially. This wasn't to last the full 90 minutes, however.
The Seagulls got their first goal back with less than 10 minutes to go. A hopeful ball over the top wasn't dealt with by the City defence, allowing Terland the opportunity to run through and finish low past Leitzig.
This served to spur the hosts on and minutes before additional time was shown, a cross directed towards goal by Terland brought the scores back level. The Foxes were somewhat fortunate to leave with a point, as Terland missed an opportunity for a hat-trick from a quick counter-attack.
It's another point on the board for City but after being in control for 80 minutes, Kirk will be disappointed to let the home side back in to the game. Leicester now look ahead to next week's fixtures against Manchester United and West Ham United before the Christmas break.