The Frenchman, driving a Citroën C3 Rally2 with new co-driver Alexandre Coria alongside, drew first blood and won the first pair of stages to open up a slender lead.
As the day wore on, the rest of the field began to pile on the pressure and a handful of drivers shared stage wins between them.
The pressure during the Jaškovo - Mali Modruš Potok speed test almost became too much for Rossel and he slipped behind hard-charging Skoda Fabia rival Kajetan Kajetanowicz with one stage to go.
However, the Pole’s spell at the top was short-lived and Rossel snatched the lead back in the final stage. Rossel’s advantage over Kajetanowicz stood at just 2.2sec as the crews arrived back in Zagreb for service.
"I am super happy with our day. We are leading this evening so it was very positive. We’ve got a long road ahead though, so we’re going to get back to work and focus on tomorrow," said the leader.
Niki Mayr-Melnhof was 27.9sec back from the leading pace in third in his M-Sport Ford Fiesta Rally2. The Austrian driver even managed to grab a maiden stage victory in SS3.
Mayr-Melnhof had no time to relax with fourth-placed Emil Lindholm breathing down his neck just 0.6sec behind. The Flying Finn was slow out of the blocks in the morning but went on to claim an impressive tally of three fastest times over the course of the day.
Frenchman Nicolas Ciamin rounded out the top-five in another Citroën car. The 23-year-old had no dramas to report from the day and trailed fellow compatriot Rossel by 30.7sec. Young Brit Chris Ingram was 45.0sec further back in sixth in another Skoda.
The challenging Croatian roads caught out a handful of drivers during the day. Hiroki Arai and Hermann Neubauer crashed their Fiesta cars out of the event during SS6, whilst Skoda man Cédric de Cecco suffered a similar fate one stage later.
- Full coverage from the Croatia Rally is available on WRC+ All Live here, including every stage broadcast as it happens as well as key interviews, features and expert analysis from the service park.