The first time the Chahars came up against each other in the league, Rahul was an unheralded legspinner and Deepak was just a Powerplay bowler. Since then, they have both established themselves as versatile performers for Mumbai Indians and Chennai Super Kings respectively.
Their fathers are brothers and their mothers are sisters. Deepak's father Lokendra Singh used to work in the Indian Air Force. It was during his father's Jaipur posting that Deepak started playing professional cricket. But Lokendra then quit his job and turned his focus on Deepak's career.
Rahul, 19 and younger to Deepak by seven years, also trained under Lokendra and aspired to become a seamer like his cousin. But Lokendra and Deepak identified Rahul's ability to spin the ball sharply in the nets and encouraged him to become a legspinner.
Deepak made heads turn when he bagged 8 for 10 on Ranji Trophy debut to bundle Hyderabad out for 21 - the lowest total in Indian domestic cricket - at just 18 years of age. In his first Ranji season, he carried Rajasthan to their first title with 30 wickets at 19.63. He was subsequently signed by Rajasthan Royals in 2011, but a spate of injuries and illnesses saw him fade away.
Rahul created a buzz in the domestic circuit when he claimed three five-wicket hauls in four Vijay Merchant Trophy Under-16 three-day games in 2013-14. Three seasons later, Rahul broke into Rajasthan's senior roster as well as the India Under-19 side.
In 2017, Deepak and Rahul were reunited at Rising Pune. Stephen Fleming and MS Dhoni initially looked at Deepak as their first-choice fast bowler, but an injury sidelined him. Rahul then replaced Deepak and made his IPL debut against Kings XI Punjab in Indore. He came away with 1 for 32 in his four overs and in the next game against Gujarat Lions he nearly did a McCullum against McCullum. He almost plucked out a blinding catch at the third-man boundary and then dismissed him with a legbreak in the next over.
Rahul got only one more game that season, but spent valuable time with Imran Tahir in the nets. Rahul will come up against his mentor, too, on Friday. Tahir has been Super Kings' top spinner in IPL 2019.
Rahul, though, was left dejected after missing the cut for the 2018 Under-19 World Cup in New Zealand; Jharkhand left-arm spinner Anukul Roy was ultimately picked ahead of him and India went onto win the tournament.
Meanwhile, Deepak, who was the top wicket-taker in the same tournament, was picked up by Super Kings for INR 80 lakh.
While Deepak became Dhoni's go-to bowler in the Powerplay and even showcased the knuckle ball last season, Rahul did not get a game. He did not start this season either, and went wicketless against Super Kings at the Wankhede, but soon found his feet and became Mumbai's premier spinner.
Rahul has a dot-ball percentage of 48.07 in IPL 2019. Only Super Kings' Harbhajan Singh has done better (49.17) among spinners who have bowled at least 30 dot balls this season.
While Mayank Markande, who was Mumbai's No.1 spinner last year, relies on wrong'uns, Rahul has been effective with his legbreak and has excellent control over it, and this enables him to bowl in the Powerplay as well as the middle overs. In the Powerplay, Rahul has grabbed only two wickets this season, but has only given away 37 runs off 30 balls. He has posed a greater wicket-taking threat from overs seven to 15, taking seven wickets in this phase while conceding 135 runs off 126 balls.
Deepak's skills in the Powerplay don't need an introduction anymore. After Super Kings' designated death bowler Dwayne Bravo was sidelined with a hamstring injury, however, Chahar has stepped up in the end overs too. It helped that he had prepared for it by tuning up his variations in the lead-up to the tournament.
All told, Deepak has bowled six overs at the slog, conceding 46 and taking four wickets. Bravo is back from injury now, but Deepak has earned Dhoni's trust to bowl at the crunch. Against Sunrisers Hyderabad on Tuesday, Deepak nailed the hard lengths and his slower balls to help limit Sunrisers to 175 for 3 in 20 overs, after they had been 151 for 2 in 17.
After the match, Shane Watson acknowledged Deepak's contribution and gushed that "Chahar's bowling has just gone through the sky".
The other Chahar's confidence is also sky-high now, and Super Kings' batting coach Michael Hussey said he's kept a close watch on Rahul. Who'll come up trumps on Friday at the Chepauk: Deepak or Rahul?
Deivarayan Muthu is a sub-editor at ESPNcricinfo