Kim Kardashian, Khloé Go Trackside for Lewis Hamilton at Monaco Grand Prix

Kim Kardashian is taking her romance with Lewis Hamilton to the fast lane ... because she showed up at Formula 1's biggest weekend looking every bit the supportive girlfriend.

The reality star was front and center at the Monaco Grand Prix qualifying session Saturday alongside sister Khloé Kardashian -- and if the photos are any indication, this wasn't some quick cameo.

Kim and Khloé practically turned the paddock into their own runway, strutting through Monaco in coordinated looks while making their way through Ferrari's team area. Kim rocked a sheer black lace top and jeans ... while Khloé kept it sleek in an all-black outfit.

The sisters later grabbed Ferrari headsets and watched the action from a premium viewing area ... putting them squarely inside the orbit of Hamilton's team as the seven-time world champion battled for position on one of Formula 1's most famous tracks.

As we've reported, the Kim and Lewis have been linked for months ... ever since their first public appearance at the Super Bowl in February. We've since seen them together all over the place ... from dinners at NOBU to a Coachella trip, PDA on the beach and handholding at a Broadway show.