The Spaniard has yet to drop a shot at Gut Larchenhof after following up blemish-free rounds of 69 and 63 with a five-under-par 67 yesterday that moved him on to 17 under for the tournament.
There was also an unexpected bonus for the 31-year-old, whose tee-off time was delayed by an hour and 40 minutes due to the threat of lightning, when rival Emiliano Grillo double-bogeyed the par-4 18th.
The Argentine, one of four joint overnight leaders alongside Larrazabal, Rafa Cabrera-Bello and Danny Willett, was just one behind Larrazabal going up the last but his slip saw him drop back to 14 under.
That left Grillo in a group of eight players sharing second place which also includes Richard Green, who produced the lowest round of the week to power up the standings. The veteran Australian had eight birdies and an eagle in his 10-under-par round of 62 .
Alongside Green and Grillo are world No 2 Henrik Stenson (66) and his fellow Swede Robert Karlsson (68), Spanish duo Carlos del Moral (66) and Cabrera-Bello (70), Thomas Bjorn (66) and Francesco Molinari (65). Nine players are on 13 under, including Scotland's Craig Lee (69) and English pair Paul Casey (63) and Willett (71)
o Copenhagen's Emily Pedersen, the European amateur title-holder, is the new British Women's Open Amateur champion. The Dane, who beat Curtis Cup Scot Gemma Dryburgh in the third round, defeated Belgium's Leslie Cloots 3&2 in the 18-hole final of the championship at Royal St George's in Kent.
It is the first time since 2009 that the title was not won by a Briton.
o A Scottish-inspired Europe team thrashed the United States 81/2-11/2 in the final set of singles to win the Palmer Cup, the students' equivalent of the Ryder Cup, by an 181/2-111/2 margin at Walton Heath in Surrey.
It was an astonishing landslide victory after the sides had been locked at 10-10 going into the last day.
Andrew Coltart, Europe's head coach, put two of three fellow Scots in his line-up, James Ross (Royal Burgess) and Grant Forrest (Craigielaw), at the top of his batting order and the move paid off with the pair both winning 3&2.
The good news spread down through the rest of the matches and lifted their team-mates. Irishman Paul Dunne won by one hole to put the Europeans three points ahead.
England's Louis Tomlinson lost to the world's top-ranked male amateur, Ollie Schniederjans, 5&3 in the American's only success. Jack McDonald (Kilmarnock Barassie), restored Europe's three-point lead with a 2&1 win and there were further European wins from Thomas Detry (Belgium), Jon Rahm (Spain), Erik Oja (Sweden) and Ricardo Gouveia (Portugal). Pep Angles (Spain) halved the last tie.