Richards made 151 off 250 balls and Hendricks 136 off 211, sharing a 258-run second-wicket partnership.
The visitors were 332-3 at stumps.
The Dolphins’ Ottniel Baartman claimed two of the three wickets to fall.
In Gqeberha, the EP Warriors posted 235-8 against the Boland Rocks, thanks to Lesiba Ngoepe (75 off 95) and Diego Rosier (58* off 104).
Rocks leg-spinner Shaun von Berg took 5-75.
In Bloemfontein, Western Province amassed 382-5 against the Free State Knights with David Bedingham scoring 161 and Tony de Zorzi 97.
Former SA U19 bowler Gerald Coetzee claimed 3-77.
In Potchefstroom, the Northerns Titans spinner Simon Harmer took 5-20 to help bowl out the North West Dragons for 147.
The Titans went on to post 118-3, with Heinrich Klaasen making 53* and Sibonelo Makhanya 33*.
In Division Two, South Western Districts ended day one of their match against the KZN Inland Tuskers on 291-8. Blayde Capell top-scored with 80.
A 132-run partnership between Jonathan Vandiar (84*) and Aubrey Swanepoel (79*) inspired the Northern Cape Heat to a commanding 315-3 against the Eastern Storm.
An undefeated 113* off 142 balls from Benjamin van Niekerk had the Mpumalanga Rhinos posting 216 against the Limpopo Impalas, who were 82-2 at stumps.
Division One:
Central Gauteng Lions lead KZN Dolphins by 332 runs
Lions: 332-3 after 96 overs; J Richards 151 (251), R Hendricks 136 (210); O Baartman 2-52, E Bosch 1-16
EP Warriors lead Boland Rocks by 235 runs
Warriors: 235-8 after 74 overs; L Ngoepe 75 (95), D Rosier 58* (104); S von Berg 5-75, H Viljoen 2-59
Western Province lead Free State Knights by 382 runs
WP: 382-5 after 96 overs; D Bedingham 161* (218), T de Zorzi 97 (190); G. Coetzee 3-77
Northerns Titans trail North West Dragons by 29 runs
Dragons: 147 after 45.2 overs; S Pillay 34 (81), N Mvelase 24 (42); S Harmer 5-50, L Williams 3-43
Titans: 118-3 after 30.3 overs; H Klaasen 53* (63), S Makhanya 33* (55); D Potgieter 1-23, D Jansen 1-27
Division Two:
South Western Districts lead KZN Inland Tuskers by 215 runs
SWD: 291-8 after B Capell 80 (68), L du Plooy 54 (134); M Erlank 3-57, T Koekemoer 2-41
Northern Cape Heat lead Eastern Storm by 315 runs
Heat: 315-3 after 83 overs; J Vandiar 84* (37), A Swanepoel 79* (85); G Thomson 1-1, N Nxumalo 1-45
Mpumalanga Rhinos lead Limpopo Impalas by 134 runs
Rhinos: 216 after 73.4 overs; B van Niekerk 113 (142), L Peters 45 (99); D Radebe 5-41, A Mokgoloboto 2-30
Impalas: 82-2 after 21 overs; T Hobson 37* (54), M Nofal 19* (40); B Xenxe 1-30
