Home side fail to make their extra man count in the second half after Marcelino's men dominated proceedings before Fazio's sending off
Benat had given Betis the lead against the run of play midway through the first half with a sumptious free kick before Alvaro Negredo scored the equalising goal for the visitors with a firm header before half time.
Negredo nearly gave Sevilla the lead in the third minute after doing brilliantly to stay onside and get on the end of Jose Antonio Reyes's through ball. However Casto's strong hand kept the scores level, and the striker could only watch as his shot looped agonisingly over the bar.
Despite winning three of their past four games, Betis started the game on the back foot as Sevilla poured men forward in search of the opening goal. Negredo and Jesus Navas both came close to scoring as the home side's defence started the game shakily.
After a chaotic opening 10 minutes, Betis began to get back into the game, with much of their good work coming from the industrious Juanma down the right-hand side.
Sevilla needed a superb interception from Federico Fazio on 20 minutes to deny Roque Santa Cruz a goalscoring opportunity after Jefferson Montero had delivered an enticing cross from the left.
Betis, however, took emphatic control of this game when Benat curled a magnificent free kick past Javi Varas from 25 yards out.
Home keeper Casto then proved his worth with a string of world-class saves from first Reyes and then Fazio as Sevilla went in search of an equaliser.
They deservedly levelled the scoreline just minutes before the break courtesy of a powerful header from Negredo. Reyes was instrumental in the goal, driving past a couple of players before feeding the ball through to Navas, who clipped a fine cross onto the head of Negredo, who was afforded far too much space by the disappointing Jose Canas.
Early in the second half, Fazio was again on hand to come to the rescue for Sevilla, dispossessing Juanma superbly as the Betis midfielder pulled back his left leg to shoot inside the area.
Fazio - Sevilla's outstanding defensive performer - was then surprisingly shown a straight red card in the 69th minute for a cynical block on Santa Cruz a full 35 yards from goal.
The controversial decision swung the game well in Betis' favour, and they very nearly took the lead from the resulting free kick, Benat whipping a fine ball into the box that was headed just wide by Santa Cruz.
After being reduced to 10 men, Sevilla began to play for the draw while Betis were throwing men forward in search of a winner.
Second-half substitute Salva Sevilla nearly made an instant impact when he played a neat one-two with Santa Cruz before showing great composure to pick Benat out in a crowded area. Betis goalscorer failed to connect with Sevilla's pass, however, and was soon crowded out by some desperate blocking from the away side.
The draw means that Betis remain in 12th place while Sevilla consolidate their place in the top half of La Liga for the time being, with a number of teams still to play this weekend.