New productions of “Medea” and “Phaedra” feature outstanding performances from Sophie Okonedo and Janet McTeer as women pushed to the edge.Tragedies are rarely absent from the London stage, but some defining theatrical titles don’t always deliver. It can be tricky to empathize with characters pushed to unimaginable extremes, and mythical landscapes can feel remote.What’s needed is a way of tapping into those works’ primal power afresh. It also helps to have performers with vocal and emotional range. London is offering two such powerhouses onstage right now: Sophie Okonedo and Janet McTeer, both Tony Award winners, though only Okonedo is in a production equal to her gifts.That would be the recently opened “Medea,” at the West End’s new in-the-round theater, @sohoplace, through April 22; performed in modern-dress without an intermission, Dominic Cooke’s expert production reminds us of the elemental fury at the heart of Euripides’ timeless play.The National Theater’s “Phaedra,” through April 8, is a new play from the Australian writer-director Simon Stone that draws from Euripides, Seneca and Racine. McTeer plays Helen, an anxious modern-day politician undone by love, as Phaedra was before her. But the tone wavers on the way to an attenuated close; the show runs nearly three hours.“Medea,” by contrast, charts a merciless 90-minute descent into the abyss, using the 1946 Robinson Jeffers adaptation from the Greek that is the play’s preferred version on Broadway.Daniels plays all the production’s male roles, including Medea’s husband, Jason.Johan PerssonWe hear the sorceress Medea before we see her, pleading for death from somewhere beneath the stage. Her husband, the explorer Jason, has transferred his affections to the daughter of the king of Corinth, leaving Medea to fester in grief and anger, and to plot literature’s most celebrated infanticide. Those children she will murder first appear onstage sweetly eating ice cream cones — but that innocence won’t last.When Okonedo does appear, sunglasses hide the eyes. “I did not know I had visitors,” she says, deadpan, taking in the playgoers seated on all sides. (The intimacy of this circular theater opened last fall by the impresario Nica Burns is among its assets.) The effect draws us further into Medea’s plight, rendering us therapists or co-conspirators — or perhaps both.The play’s chorus consists of three women of Corinth seated in the audience who speak up now and again to voice their alarm. But Cooke’s primary innovation is to cast Ben Daniels, a London stage veteran, as all the play’s men. Seen before he speaks, Daniels circles the perimeter of the auditorium in silent slow-motion before stepping into the space to play a smugly dismissive Jason, or any of the other roles. The actor puts a deliciously camp spin on the Athenian king, Aegeus, in marked contrast to Jason’s knife-wielding machismo.The suggestion is of a male-dominated world in which the high-born Medea is doomed by her gender. Her fury, though, is directed at Jason specifically, and she commits the barbaric murder of their sons unseen, emerging afterward in embittered triumph.Throughout, Okonedo displays the suppleness of thought, and the wit, with which Medea surely once bewitched Jason, and the remorseless logic that has led to her monstrous deeds. Medea may go to extremes unknown to most of us, but this production keeps you on her side every step of the way.Chloe Lamford’s set for “Phaedra” at the National Theater encases the action in an revolving cube.Johan PerssonIt’s easy to imagine a younger McTeer as Medea, a role well matched to this fearless actress’s elegantly smoky voice and imposing physicality. As the sleekly attired Helen in “Phaedra,” she suggests a woman of wealth and power who knows how to work a room.That self-assurance is why it’s startling to watch her composure crack across a fitful evening that might work better if the production felt less remote. It’s a challenge to connect with the characters through the revolving cube of Chloe Lamford’s enclosed set.Not only must the actors be heavily amplified to be heard, but there are long blackouts while we wait for the various locations to be revealed — among them, a London restaurant, a field of reeds in the English countryside, or the rough Moroccan terrain of the play’s end.The characters at the start talk very fast, as if challenging the audience to keep up. But the gabble ceases with the unexpected appearance of Sofiane (Assaad Bouab) whose father, Ashraf, Helen’s lover, was killed in a car crash; Helen was in the vehicle at the time of the incident, which occurred when Sofiane was still a child.In “Phaedra,” Janet McTeer, left, plays Helen, who has an affair with the son of a former lover, played by Assaad Bouab.Johan PerssonHelen transfers her dormant feelings for Ashraf to the now-grown, and flirtatious, Sofiane, unaware that he is soon also bedding Helen’s daughter, Isolde (Mackenzie Davis, in an accomplished stage debut).The play surprises with its bursts of humor. Playing Helen’s sharp-tongued diplomat husband, the wonderful Paul Chahidi brings whiplash timing to a series of stinging takedowns of his philandering wife, who revels in feeling young again. (It would be helpful, though, to know more about Helen’s political life than the play lets on.)But for all McTeer’s considerable magnetism, this “Phaedra” feels like a messy story of romance gone wrong, modishly dressed up. Helen and her world may belong to the here and now, but it’s the centuries-old tale of Medea that really strikes at the heart anew. More