In recent years, Formula One’s defining rivalry has seemed clear: Lewis Hamilton of Mercedes (and before that, McLaren) vs. Sebastian Vettel of Ferrari (and before that, Red Bull). The two have combined to win nine of the past 11 world driver’s championships, with the only interlopers being Jenson Button in 2009 and Nico Rosberg, another of Hamilton’s most bitter rivals, in 2016. Hamilton and Vettel finished 1-2 in each of the previous two seasons’ standings, so the path to the F1 title seemed very likely to go through them in 2019 as well.

This year, though, only one of the two has held up his end of the bargain. Hamilton currently leads the championship, 63 points clear of Mercedes teammate Valtteri Bottas. But instead of vying for the title as well, Vettel is all the way back in fifth place, 115 points behind his English archrival. The German hasn’t finished so low in the standings since 2014, his tumultuous final season with Red Bull.

With the recent breakout of Vettel’s Ferrari teammate, Charles Leclerc — the 21-year-old rising star who just grabbed his first two F1 career wins in back-to-back races — there are legitimate questions as to which driver Hamilton should be more concerned about as a rival going forward. In fact, Leclerc has done so well in his second F1 season that the four-time world champ Vettel might not even be the No. 1 driver on his own team anymore.

That this is up for debate speaks volumes about Leclerc’s meteoric ascent. The Monégasque phenom was a teenager in Formula Two just a couple of years ago, impressing as a test driver but failing to nail down a seat at a prestige team for his rookie F1 season. Leclerc joined Alfa Romeo-Sauber for 2018 instead and flashed his potential with a very strong qualifying performance against teammate Marcus Ericsson, whom he started ahead of on the grid 17 times in 21 races (81 percent) last season. But on race days, Leclerc finished slightly worse than he started, beat Ericsson only 57 percent of the time (after adjusting for grid position) and notched only 39 points in the championship, finishing a distant 13th.

(Besides, Ericsson wasn’t exactly the toughest competition; he didn’t secure an F1 ride in 2019 and currently competes in the IndyCar series.)

Still, Ferrari saw the talent evident in Leclerc’s performance and pegged him to replace folk hero Kimi Räikkönen as Vettel’s No. 2 going into 2019. But Vettel’s place atop the pecking order seemed secure. He had spent most of the previous four seasons driving circles around Räikkönen, beating the 2007 world champion in 67 percent of qualifying runs and 73 percent of races. Although he couldn’t quite outduel Hamilton, finishing an average of 101 points behind him in the overall standings during those seasons, Vettel was still very competitive — and hopeful that a new 2019 design package would bring the Prancing Horse its first championship (as either a constructor or for its drivers) since the late 2000s.

The early returns seemed like business as usual. Although Mercedes opened the season with an eight-race winning streak, as Hamilton took six of those checkered flags himself, Vettel had also outdriven Leclerc 12 times in 14 chances (including both qualifying and races) over the first seven events on the schedule. (The only exception was the Bahrain Grand Prix, where Leclerc won the pole and finished third to Vettel’s fifth.) Vettel even technically crossed the finish line first in Canada, only to see Hamilton be awarded the win because of a controversial penalty assessed when Vettel swerved back onto the track after a missed turn.

Ever since that moment, however, Leclerc has surged past his older, more decorated teammate at a breathtaking pace. If we build an Elo rating using the same head-to-head approach that I used in this story about Fernando Alonso from last summer — which just compared teammate performances with each other (to control for differences in constructor quality) and gave qualifiers half-weight as compared with races — Leclerc moved past Vettel for the very first time in his career when he won the Italian Grand Prix last Sunday:

This teammate-versus-teammate approach isn’t perfect, particularly when it involves drivers who haven’t changed teams much. But it is able to infer one driver’s performance from how often he beats another driver of an established ability level. And Vettel is certainly established; he went into the season (and his partnership with Leclerc) with the third-best rating of any driver in the 2019 field, trailing only Hamilton and Red Bull’s Max Verstappen — another Leclerc-esque wunderkind (also 21 years old) trying to end the Hamilton-Vettel hegemony atop the F1 standings.

For Leclerc’s part, he has risen from a relatively mediocre head-to-head Elo of 1454 after the Canadian Grand Prix on June 9 to a 1529 mark (fourth-best in the field) after back-to-back victories in Belgium and Italy these past two weeks. He has now outperformed Vettel in each of the past seven qualifying sessions and five of the past seven races (the only exceptions being Germany and Hungary). By coolly fending off the best attacks Hamilton and Bottas could throw at him, the “unflappable” Leclerc gave Ferrari a win at Monza — its home race — for the first time since Alonso did it in 2010. Along the way, he has given Vettel more fits than just about any teammate in his entire career:

Vettel’s teammates seldom challenge as much as Leclerc Head-to-head comparisons between Sebastian Vettel and teammates — in qualifying and races — by season, 2007-19 Qualifying Races* Season Team Teammate H2H Wins Win% H2H Wins Win% Champ. Rk 2007 Sauber/Toro Rosso Heidfeld/Liuzzi 3 38% 3 38% 14th 2008 Toro Rosso S. Bourdais 14 78 13 72 8th 2009 Red Bull Racing Mark Webber 14 82 8 47 2nd 2010 Red Bull Racing Mark Webber 13 68 11 58 1st 2011 Red Bull Racing Mark Webber 16 84 14 74 1st 2012 Red Bull Racing Mark Webber 12 60 14 70 1st 2013 Red Bull Racing Mark Webber 17 89 17 89 1st 2014 Red Bull Racing Daniel Ricciardo 9 47 6 32 5th 2015 Scuderia Ferrari Kimi Räikkönen 15 79 16 84 3rd 2016 Scuderia Ferrari Kimi Räikkönen 9 43 15 71 4th 2017 Scuderia Ferrari Kimi Räikkönen 15 75 16 80 2nd 2018 Scuderia Ferrari Kimi Räikkönen 15 71 12 57 2nd 2019 Scuderia Ferrari Charles Leclerc 6 43 8 57 5th Total 158 68 153 65 *Race performance is adjusted slightly for starting grid position Source: racing-reference.info

Despite the back-to-back losses, Mercedes isn’t exactly worried about Leclerc chasing Hamilton down for the title. The quick circuits of the past two races probably favored Ferrari, with the superior straight-line speed of its SF90 car. And even after Leclerc’s big breakthrough, he remains 102 points behind Hamilton (and 39 behind Bottas) in the standings, with Ferrari running 154 behind Mercedes in the team tally as they look ahead to the season’s final seven races.

But although Leclerc’s wins didn’t make much impact on the overall championship picture, they may have represented something of a turning point in F1 history. Going into 2019, Vettel had outqualified his teammates — a strong group that included Räikkönen, Daniel Ricciardo and Mark Webber — 69 percent of the time and outraced them 66 percent of the time in his career. Against Leclerc this season, those numbers are only 43 percent and 57 percent, respectively, and getting worse by the moment.

Vettel entered the season as a championship contender and the clear standard-bearer for the sport’s most storied team. Now his place is in doubt. With another year left on his contract, Vettel probably isn’t going anywhere (despite tabloid rumors to the contrary), but it’s hard not to juxtapose Leclerc’s recent surge against Vettel’s growing tendency toward crucial errors and on-track decisions that put other drivers at risk. So the biggest question for the season’s home stretch isn’t whether Leclerc is the future of the sport — that now seems established — but rather, it’s whether Vettel can avoid being left in the past.