Star striker Lionel Messi scored his 50th international goal to guide Argentina to a 2-0 win over Bolivia in a 2018 World Cup qualifier.The win helped Argentina jump to the third spot in the South American group with 11 points from six matches. They are two points behind joint leaders Ecuador and Uruguay.Argentina defender Gabriel Mercado opened the scoring in the 21st minute against Bolivia here on Tuesday.He also scored the winning goal in their 2-1 away victory over Chile on Thursday. Argentina won a penalty in the 29th minute when Ronald Eguino fouled midfielder Ever Banega.Messi converted the penalty to net his 50th goal for Argentina. He is now six behind Gabriel Batistuta’s all-time highest list for Argentina.The top four teams in the 10-nation group qualify for the 2018 World Cup finals, to be held in Russia, while the fifth-placed side plays an intercontinental playoff.